Generics

Basilisk doesn't seem to handle rather basic examples involving generics, for example:

from typing import assert_type

class P: ...

def duplicate[T](value: T) -> tuple[T, T]:
    return value, value

assert_type(duplicate(P()), tuple[P, P])

Basilisk fails this assertion and incorrectly infers tuple[T, T] (leaking type variables) instead of tuple[P, P].

Using list[T] or int | T in the return type leads to similar failures.

It also seems to rely on the fact that type variables are capitalized? It fails this assertion and infers t instead of int:

def identity[t](value: t) -> t:
    return value

assert_type(identity(1), int)

Start by reproducing the generic-function and assert_type examples from the issue, then trace Basilisk's generic inference and type-variable handling. Done means the examples infer tuple[P, P] and int rather than leaking or preserving the type variables.