Exempt base-dictated Any positions in @override methods from explicit-any

[nitishagar]

Fixes #4548

Problem

With explicit-any = "error", a @typing.override method whose base signature is annotated with Any must repeat that Any — narrowing or dropping it would break the override — yet the rule fired on exactly those annotations:

import json
from typing import Any, override

class CustomEncoder(json.JSONEncoder):
    @override
    def default(self, o: Any) -> Any:   # 2 explicit-any errors
        return super().default(o)

The signature is fixed by typeshed's json.JSONEncoder.default ((self, o: Any) -> Any), so the diagnostic points at code that cannot be changed. Ruff exempts @override methods in its equivalent lint (ANN401) for the same reason.

Change

• The binding step already knows is_override (name-only decorator check) when it registers method annotations; those annotations now carry the method's name when they belong to an @override method.
• Parameter and return annotations report explicit-any from solve_annotation (which has the class context) instead of expr_untype; a position is exempt only when the annotation is exactly Any and the corresponding base position is explicitly annotated Any:
  • params matched by name (*args/**kwargs and return positions included),
  • async base returns unwrapped from Coroutine[Any, Any, T],
  • every overload of an overloaded base considered.
• Everything else still reports: undictated positions, methods without @override, @override with no base member (bad-override still fires), base positions that merely lack annotations, and nested Any like list[Any].

The base's own explicit Anys still report when the base is user code in the checked project (in the issue's case the base is in typeshed and not checked) — only the dictated override positions are exempt.

Test plan

• 12 new testcase!s in pyrefly/lib/test/inference.rs covering: exemption (plain/args-kwargs/overload/typing_extensions/async), still-reporting (undictated positions, no decorator, no base member, unannotated base param, nested Any, per-position granularity)
• Issue repro checks clean with explicit-any = "error"
• cargo test -p pyrefly --lib -- --skip test::lsp green (the two missing-source LSP interaction failures are pre-existing on main)
• Formatting/linting clean