[Shanmukh-l33t]

Fixes #22398.

visit_instance() special-cases Instance <: Callable / Overloaded by following the __call__ member (mypy/subtypes.py). When that member (transitively) refers back to its own class — class C: __call__: C — the check recurses forever, so

from typing import Callable

class C:
    __call__: "C"

def h(cb: Callable[[], int]) -> None: ...

h(C())

crashes mypy with RecursionError on pure-Python builds and segfaults (exit 139) on compiled wheels, exactly as reported in the issue.

Fix

Track the TypeInfos whose __call__ is currently being followed in SubtypeContext (shared down the whole subtype query, since each recursion level constructs a fresh SubtypeVisitor but keeps the context). When the chain loops back to a class already being followed, return False: such an instance cannot be called at runtime either, so it is simply not a subtype of that Callable type. The caller then reports the normal error the issue asks for:

repro.py:12: error: Argument 1 to "h" has incompatible type "C"; expected "Callable[[], int]"
repro.py:12: note: "C.__call__" has type "C"

This complements #22362 (which guards the check_call() path in checkexpr.py); this path is subtypes.py only, as noted in the issue. The guard is scoped to the FunctionLike branch and popped in a finally, so it cannot leak into unrelated checks; sibling branches (protocol __call__, nominal checks) are untouched.

Covered variants: direct (__call__: C), Optional[C], Self, generic G[list[T]] (type args grow each round, so a pair-based guard would not fire), mutually-referencing X/Y, plus assignment-position checks, and positive controls (def __call__ classes still check clean).

Testing

• New data-driven test testSubtypeOfCallableWithSelfReferentialCallAttribute in test-data/unit/check-classes.test: fails at parent 5dc2840 with RecursionError / INTERNAL ERROR (the exact reported crash) and passes with the fix.
• Full suite (pytest mypy/test -q -n 2): 12574 passed, 362 skipped, 10 xfailed; the 3 failures (test_find_sources_exclude, 2× testoutput JSON-parallel) are environment-only — they spawn python -m mypy.build_worker in a venv where mypy is not pip-installed — and reproduce identically with this change stashed.
• Targeted subsets: check-classes.test 619 passed / 1 xfailed; check-callable, check-expressions, check-protocols, check-generic-subtyping 499 passed.
• black --check, ruff check, and mypy --config-file mypy_self_check.ini mypy/subtypes.py all clean.

Note: I built this against master 5dc2840 (the revision in the issue) before #22362 landed; the two changes touch different files, so they merge independently.