Fix inheritance edge cases for type parameter resolution

[brentyi]

Fixed some errors when resolving type parameters.

(1) Reusing the same TypeVar in multiple levels of an inheritance tree is allowed in Python, but was previously broken:

import dataclasses
from typing import Generic, TypeVar
import tyro

T = TypeVar("T")

@dataclasses.dataclass(frozen=True)
class A(Generic[T]):
    x: T

@dataclasses.dataclass(frozen=True)
class B(A[int], Generic[T]):
    y: T

# now works!
args = tyro.cli(B[str])

(2) We now correctly traverse inheritance trees when resolving type parameters that are used in __init__ and __new__ signatures. This fixes #229:

from pydantic import BaseModel
import tyro

class AConfig(BaseModel):
    a: int

class AModel[TContainsAConfig: AConfig]:
    def __init__(self, config: TContainsAConfig):
        self.config = config

class ABConfig(AConfig):
    b: int

class ABModel[TContainsABConfig: ABConfig](AModel[TContainsABConfig]):
    pass

class ABCConfig(ABConfig):
    c: int

class ABCModel(ABModel[ABCConfig]):
    pass

# now works!
tyro.cli(ABCModel)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.82%. Comparing base (6761eed) to head (8265262).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #230   +/-   ##
=======================================
  Coverage   99.82%   99.82%           
=======================================
  Files          28       28           
  Lines        2308     2320   +12     
=======================================
+ Hits         2304     2316   +12     
  Misses          4        4           

Flag	Coverage Δ
unittests	99.82% <100.00%> (+<0.01%)	⬆️

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