COMPAT: ensure proper extension dtype's don't pickle the cache
xref #16201 
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=h1) Report
> Merging [#16207](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/39cc1d0685481c77115f061d856cc60c1e59c8c2?src=pr&el=desc) will **increase** coverage by `0.02%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16207/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16207      +/-   ##
==========================================
+ Coverage   90.86%   90.89%   +0.02%     
==========================================
  Files         162      162              
  Lines       50867    50879      +12     
==========================================
+ Hits        46222    46246      +24     
+ Misses       4645     4633      -12
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.67% <100%> (+0.02%)` | :arrow_up: |
| #single | `40.31% <41.66%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/dtypes/dtypes.py](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2R0eXBlcy5weQ==) | `95.62% <100%> (+0.58%)` | :arrow_up: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `90.68% <0%> (-0.35%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.35% <0%> (+1.81%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=footer). Last update [39cc1d0...7dc8f9f](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=h1) Report
> Merging [#16207](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/39cc1d0685481c77115f061d856cc60c1e59c8c2?src=pr&el=desc) will **increase** coverage by `0.02%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16207/graphs/tree.svg?height=150&width=650&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16207      +/-   ##
==========================================
+ Coverage   90.86%   90.89%   +0.02%     
==========================================
  Files         162      162              
  Lines       50867    50879      +12     
==========================================
+ Hits        46222    46246      +24     
+ Misses       4645     4633      -12
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.67% <100%> (+0.02%)` | :arrow_up: |
| #single | `40.31% <41.66%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/dtypes/dtypes.py](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2R0eXBlcy5weQ==) | `95.62% <100%> (+0.58%)` | :arrow_up: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `90.68% <0%> (-0.35%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.35% <0%> (+1.81%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=footer). Last update [39cc1d0...7dc8f9f](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=h1) Report
> Merging [#16207](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/39cc1d0685481c77115f061d856cc60c1e59c8c2?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `81.25%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16207/graphs/tree.svg?token=eZ4WkYLtcO&width=650&src=pr&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16207      +/-   ##
==========================================
+ Coverage   90.86%   90.86%   +<.01%     
==========================================
  Files         162      162              
  Lines       50867    50881      +14     
==========================================
+ Hits        46222    46235      +13     
- Misses       4645     4646       +1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.65% <81.25%> (ø)` | :arrow_up: |
| #single | `40.31% <25%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/dtypes/dtypes.py](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2R0eXBlcy5weQ==) | `94.92% <81.25%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=footer). Last update [39cc1d0...8d43cba](https://codecov.io/gh/pandas-dev/pandas/pull/16207?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
