Fix: slow multipart parsing for huge files with few CR/LF characters for 2.2.x branch

[tkgup]

• fixes GHSA-hrfv-mqp8-q5rw on 2.2.x which support python 3.7

Fix: slow multipart parsing for huge files with few CR/LF characters for 2.2.x branch

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.

[davidism]

2.2.x is no longer maintained. Only the latest feature branch (3.0.x) is maintained. Python 3.7 is end of life. You should update to newer versions of Python and dependencies.