Partial support for type parameters in class methods

[brentyi]

The goal of this PR is to resolve type parameters in class methods like this:

import tyro

class Base[T]:
    @classmethod
    def f(cls, x: T) -> T:
        print(x)
        return x

class Subclass(Base[int]):
    pass

tyro.cli(Subclass.f)  # Should have argument `--x INT`

tyro.cli(Base[int].f) will still not work, because we can't distinguish between Base[int].f and Base.f at runtime. The "What's not supported" doc has been updated to explain this: https://brentyi.github.io/tyro/whats_supported/#what-s-not-supported

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.78%. Comparing base (b5d8bc7) to head (834d051).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #238      +/-   ##
==========================================
- Coverage   99.78%   99.78%   -0.01%     
==========================================
  Files          28       28              
  Lines        2329     2326       -3     
==========================================
- Hits         2324     2321       -3     
  Misses          5        5              

Flag	Coverage Δ
unittests	99.78% <100.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.