Improve tomllib startup time

[vstinner]

Currently, importing tomllib takes 9.5 ms. I wrote a proof-of-concept which defers importing regular expressions: with this change, importing tomllib now only takes 0.9 ms (10.6x faster).

Benchmark on Python built in release mode (gcc -O3) on Fedora 43:

$ python -m pyperf command -- ./python -S -c 'pass'
command: Mean +- std dev: 7.77 ms +- 0.75 ms
$ python -m pyperf command -- ./python -S -c 'import tomllib'
command: Mean +- std dev: 17.3 ms +- 0.3 ms

With my change:

$ python -m pyperf command -- ./python -S -c 'import tomllib'
command: Mean +- std dev: 8.70 ms +- 0.82 ms

This optimization is motivated by PEP 829: Structured Startup Configuration via .site.toml Files discussion which proposes using tomllib at Python startup.

Linked PRs

• gh-147991: Speed up tomllib import time #147992