Merge PR pypa#1166: PEP 639 compliance

This merges the PEP 639 compliance changes from PR pypa#1166:
- Updates license format from 'license.file' to 'license = "MIT"'
- Bumps setuptools requirement to >=77.0.3 for PEP 639 support
- Removes 'License :: OSI Approved :: MIT License' classifier (redundant with new license field)
- License file auto-detection relies on setuptools defaults

Co-authored-by: Dimitri Papadopoulos <[email protected]>

Author: RonnyPfannschmidt

pyproject.toml

@@ -3,7 +3,7 @@
 [build-system]
 build-backend = "_own_version_helper:build_meta"
 requires = [
-  "setuptools>=61",
+  "setuptools>=77.0.3",
   "vcs-versioning",
   'tomli<=2.0.2; python_version < "3.11"',
 ]