DOC: fix errors/warnings in running code blocks
Cleaning up errors / warnings in the doc build, related to the ipython code blocks:

- put a section about hdf5 and Panel in verbatim code blocks + added some `:okwarning:` for Panel (will need to be properly cleaned up when Panel is removed)
- fixed cases that raised deprecation warning for `TimedeltaIndex.fillna()` with integers
- reworded case that raised deprecation warning about passing integers + timezone to DatetimeIndex
- `pd.core.config` doesn't exist anymore -> removed that call + made the actual example verbatim
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26076?src=pr&el=h1) Report
> Merging [#26076](https://codecov.io/gh/pandas-dev/pandas/pull/26076?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/5a150694731d2ecce670cca65760c472338a04fa?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26076/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26076?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26076      +/-   ##
==========================================
- Coverage   91.89%   91.89%   -0.01%     
==========================================
  Files         175      175              
  Lines       52509    52509              
==========================================
- Hits        48255    48251       -4     
- Misses       4254     4258       +4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.45% <ø> (ø)` | :arrow_up: |
| #single | `40.74% <ø> (-0.14%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26076?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26076/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `75% <0%> (-12.5%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26076/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.79% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26076?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/26076?src=pr&el=footer). Last update [5a15069...fbba132](https://codecov.io/gh/pandas-dev/pandas/pull/26076?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/26076?src=pr&el=h1) Report
> Merging [#26076](https://codecov.io/gh/pandas-dev/pandas/pull/26076?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/5a150694731d2ecce670cca65760c472338a04fa?src=pr&el=desc) will **increase** coverage by `0.04%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26076/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26076?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26076      +/-   ##
==========================================
+ Coverage   91.89%   91.94%   +0.04%     
==========================================
  Files         175      175              
  Lines       52509    52427      -82     
==========================================
- Hits        48255    48204      -51     
+ Misses       4254     4223      -31
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.5% <ø> (+0.05%)` | :arrow_up: |
| #single | `40.73% <ø> (-0.15%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26076?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26076/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `75% <0%> (-12.5%)` | :arrow_down: |
| [pandas/util/\_doctools.py](https://codecov.io/gh/pandas-dev/pandas/pull/26076/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX2RvY3Rvb2xzLnB5) | `12% <0%> (-0.88%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26076/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.79% <0%> (-0.13%)` | :arrow_down: |
| [pandas/core/computation/ops.py](https://codecov.io/gh/pandas-dev/pandas/pull/26076/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tcHV0YXRpb24vb3BzLnB5) | `95.62% <0%> (-0.04%)` | :arrow_down: |
| [pandas/core/computation/align.py](https://codecov.io/gh/pandas-dev/pandas/pull/26076/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tcHV0YXRpb24vYWxpZ24ucHk=) | `97.8% <0%> (-0.03%)` | :arrow_down: |
| [pandas/core/reshape/melt.py](https://codecov.io/gh/pandas-dev/pandas/pull/26076/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9tZWx0LnB5) | `97.47% <0%> (-0.03%)` | :arrow_down: |
| [pandas/plotting/\_core.py](https://codecov.io/gh/pandas-dev/pandas/pull/26076/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb3JlLnB5) | `83.76% <0%> (-0.02%)` | :arrow_down: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/26076/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `90.61% <0%> (-0.01%)` | :arrow_down: |
| [pandas/core/sparse/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26076/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3BhcnNlL2ZyYW1lLnB5) | `95.49% <0%> (-0.01%)` | :arrow_down: |
| [pandas/core/sorting.py](https://codecov.io/gh/pandas-dev/pandas/pull/26076/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc29ydGluZy5weQ==) | `98.29% <0%> (-0.01%)` | :arrow_down: |
| ... and [35 more](https://codecov.io/gh/pandas-dev/pandas/pull/26076/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26076?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/26076?src=pr&el=footer). Last update [5a15069...ec8396d](https://codecov.io/gh/pandas-dev/pandas/pull/26076?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 small comment. add Panel to code-blocks in 2 places or followup is ok. > small comment. add Panel to code-blocks in 2 places or followup is ok.

Yeah, we indeed need to convert those to actual code-blocks at some point. But there are still some other occurrences as well, so will leave that for a separate PR.