B006: ignore when type hints suggests immutability.

When passing configurations to functions, it is quite annoying to have to do the whole Optional[Mapping[str, Any]] = None dance. It would be nice if it was possible to allow mutable defaults, when the type hints indicate immutability. (possibly via some --strict/--non-strict flag.)

from collections.abc import *

def foo(
    configA: Mapping[str, Any] = {},         # needn't raise B006
    configB: MutableMapping[str, Any] = {},  # should raise B006
    configC: dict[str, Any] = {},            # should raise B006
    seqA: Sequence[str] = [],                # needn't raise B006
    seqB: MutableSequence[str] = [],         # should raise B006
    seqC: list[str] = [],                    # should raise B006
    setA: Set[str] = set(),                  # needn't raise B006
    setB: MutableSet[str] = set(),           # should raise B006
    setB: set[str] = set(),                  # should raise B006
): ...

The reasoning is that the type checker should catch mutable behavior, and the benefit is obviously shorter function bodies that avoid the configA = {} if configA is None else configA boilerplate.

No file or test is named. Start by locating the existing B006 check and reviewing how its current mutable-default cases are tested; compare the issue's immutable and mutable type-hint examples. Done means defining the strictness behavior and covering the accepted and rejected annotations with tests.