provide and support mypy 2.x in bundled tools

[cburroughs]

We currently have:

pants/src/python/pants/backend/python/typecheck/mypy/subsystem.py

Line 83 in ccb7f45

default_requirements = ["mypy>=0.961,<2"]

The changelog is at https://mypy-lang.blogspot.com/2026/05/mypy-20-relased.html . This is mostly 2.x in semver sense (defaults changed), not a radical re-write. I think it would be reasonable (in a future release after 2.33 that already is likely to upgrade the mypy version) to simply update this to <3. However I do think we should first fix:

• support "PRAGMA synchronous=OFF" design from mypy #23232
• evaluate options for reacting to new mypy db sharding options #23352