Fix variadic ParamSpec expansion crash

[KirschBluteX]

Fixes #21778.

ExpandTypeVisitor.visit_parameters previously expanded parameter types independently from their kinds and names. A starred Unpack[TypeVarTuple] could therefore reach TypeVarTuple expansion with a concrete tuple replacement and raise NotImplementedError. A nested expansion could also produce a concrete prefix, a residual unpack, and a concrete suffix; emitting that suffix as positional parameters after *args created an invalid parameter layout.

This change expands a direct starred TypeVarTuple unpack while updating argument types, kinds, and names in lockstep. Concrete tuple items become positional parameters. When expansion leaves a residual variadic, that unpack and its suffix remain grouped as one starred tuple, preserving nested ParamSpec call semantics and the existing error-recovery path.

The regression tests cover the reported ParamSpec-based context-manager decorator, verify both the with-target and decorated call types, and exercise a nested print_args(0, *args, "end") forwarding call whose revealed result retains the residual TypeVarTuple and suffix.

Tests:

• python -m pytest -n0 mypy/test/testcheck.py::TypeCheckSuite::check-parameter-specification.test
• python -m pytest -n0 mypy/test/testcheck.py::TypeCheckSuite::check-typevar-tuple.test -k "ParamSpec or Unpack"
• python -m pytest -n0 mypy/test/testtypes.py -k expand
• python -m mypy --config-file mypy_self_check.ini mypy/expandtype.py
• python -m ruff check mypy/expandtype.py
• Targeted pre-commit hooks: trailing-whitespace, end-of-file-fixer, black, ruff-check, codespell
• GitHub CI: 25 checks passed

[TheMuffinMan1320]

Looks good!

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅