Add test coverage for Python 3.12+ type params and PEP 701 f-strings

[Emilianocarfu88]

Description

Adds test coverage for Python 3.12+ syntax that was thin in the suite, focused on how
PEP 695 type parameters (incl. PEP 696 defaults, *TypeVarTuple/**ParamSpec) and
PEP 701 f-strings interact with Black's line splitting and comment handling.

New data-driven cases (auto-discovered by test_simple_format, so each also runs Black's
built-in AST-equivalence, idempotency/stability, preview, and line-length-1 checks):

• tests/data/cases/type_params_comments.py — comments inside type-param brackets
  (inline, leading/standalone, on bounds and constraint tuples).
• tests/data/cases/type_param_defaults_comments.py — PEP 696 defaults with comments and
  wrapping.
• tests/data/cases/fstring_pep701_comments.py — comments in multiline interpolations,
  nested/quote-reuse f-strings, format specs, = debug, call-argument splitting.
• tests/data/cases/type_params_line_split.py — overflowing type-param lists,
  bounds/constraints, combined type-param + argument + return-type splitting.

Property-based tests:

• tests/test_pep695_701_properties.py — targeted Hypothesis strategies for type-param
  lists and f-strings asserting idempotency (assert_stable) and AST safety
  (assert_equivalent) across varied modes (line lengths incl. 1, preview, magic-comma,
  string normalization). Every generated example is compile()-checked first so a
  strategy bug can't masquerade as a Black bug. Mirrors the deterministic settings of
  scripts/fuzz.py.

Regression test:

• tests/test_regression_type_params.py — a strict-xfail pinning Magic trailing comma does not explode a type-parameter list containing *TypeVarTuple / **ParamSpec #5243 (a magic trailing
  comma fails to explode a type-param list once it contains *TypeVarTuple/**ParamSpec).
  It asserts the desired exploded output, so when the bug is fixed the test XPASSes and the
  strict marker turns that into a failure, prompting promotion to a normal data case.

All expected # output blocks were generated by running Black itself, never hand-written.

Checklist

• Added tests
• No user-facing changes, so no CHANGES.md entry (happy to add one if preferred)

Relates to #5243.