gh-118761: improve import time for pickle

[picnixz]

We can remove the re import which takes quite a long time. Benchmarks were performed on a RELEASE build (no PGO, no LTO). It's a bit hard to have stable numbers with -X importtime, so I'm only using the hyperfine benchmarks.

PR

$ hyperfine --warmup 8 "./python -c 'import pickle'"
Benchmark 1: ./python -c 'import pickle'
  Time (mean ± σ):       7.8 ms ±   0.3 ms    [User: 6.6 ms, System: 1.3 ms]
  Range (min … max):     7.4 ms …   9.8 ms    337 runs

Main

$ hyperfine --warmup 8 "./python -c 'import pickle'"
Benchmark 1: ./python -c 'import pickle'
  Time (mean ± σ):       9.7 ms ±   0.3 ms    [User: 8.3 ms, System: 1.4 ms]
  Range (min … max):     9.3 ms …  12.6 ms    282 runs

Since something that is no more present in the global namespace is removed, I've added a NEWS entry and a detailed changelog.

• Issue: Improve import time of various stdlib modules #118761

[picnixz]

I'll merge this one tomorrow (and will check if removing isidentifier() improves a bit performances). I want to keep the first commit message as it indicates that re is now removed from the global namespace (it should never have been accessed from outside but we never know; maybe someone has been patching that attribute for whatever reason in their test suite).

EDIT: no micro-optimization so leaving the numbers as is

[picnixz]

As a follow-up, I can also improve the import time of pickletools once I've merged this one (reason is that pickletools imports re and pickle so if I just change pickletools now, without this PR, then we won't see any improvements at all).

[picnixz]

@vstinner I plan to merge this one with the following commit message:

Importing `pickle` is now roughly 25% faster.

Importing the `re` module is no longer needed and
thus `re` is no more implicitly exposed as `pickle.re`.

and following title:

Improve import time of the `pickle` module.

[vstinner]

LGTM

[AA-Turner]

@picnixz tiny note for the future -- when merging, try not to end the titles of commit messages with full stops ('.'), as it doesn't work well with the auto-appended PR reference: ff3e145