[CLN] More cython cleanups, with bonus type annotations
A few places where string formatting is modernized

Removed remaining `# cython: profile=False` comments

The main (and possible controversial) thing done here is changing some functions to use type-hint syntax.  The affected functions are all currently `cpdef`, but are never used in cython, so _should_ only be `def`.  But cython's syntax does not allow for specifying a return type in `def` functions, so this is the cleanest way to remove unnecessary `cpdef` without losing typing.  (some discussion of this occurred in #22180)
Out of curiosity how are you verifying that the `cpdef` functions are only being called from Python? Manual exercise or is there a tool to help identify? > Out of curiosity how are you verifying that the cpdef functions are only being called from Python? Manual exercise or is there a tool to help identify?

Just text search within the file.  Since the relevant functions aren't exposed in a .pxd file, there is no risk of them being called from a different cython file. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22283?src=pr&el=h1) Report
> Merging [#22283](https://codecov.io/gh/pandas-dev/pandas/pull/22283?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/e2e1a1051576a48f210ce17272fc24b90ebcf24a?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22283/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/22283?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #22283   +/-   ##
=======================================
  Coverage   92.04%   92.04%           
=======================================
  Files         169      169           
  Lines       50782    50782           
=======================================
  Hits        46742    46742           
  Misses       4040     4040
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.45% <ø> (ø)` | :arrow_up: |
| #single | `42.3% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22283?src=pr&el=continue).
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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22283?src=pr&el=footer). Last update [e2e1a10...3300de1](https://codecov.io/gh/pandas-dev/pandas/pull/22283?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @jreback would this be easier if I separated the no-profile comments into an isolated PR? no just haven’t had a chance to look yet @jreback gentle ping; got your OK last week think this was ok, can you rebase Rebased; circleCI fail is hypothesis timeout Rebased+green thanks!