Broken import w/ pip 24.1

[brendan-morin]

Hi! Thanks for the awesome project! It appears things have broken w/ pip 24.1 (released June 20th):

requirementslib/src/requirementslib/models/requirements.py

Line 42 in 591f194

LegacySpecifier,

See pip changes in src/pip/_vendor/packaging/specifiers.py to remove LegacySpecifier: https://github.com/pypa/pip/compare/24.0..24.1#diff-cebb4f08d8c2fe0cc348a9239c24aab09c968e464a0d2e8db8b5dc78b2dd1a9aL227