fix: type LEDPattern map_index callback as int

[Amidwestnoob]

Fixes #168

Problem

LEDPattern.map_index stubs typed the callback as
Callable[[SupportsInt | SupportsIndex, SupportsInt | SupportsIndex], int].
Callers pass (length: int, idx: int) -> int. Callback parameters are
contravariant, so Pylance/mypy reject valid mappers.

Fix

Bind MapIndex with py::typing::Callable<py::int_(py::int_, py::int_)> so
generated stubs emit Callable[[int, int], int]. Own the Python callable as
shared_ptr<py::function> with gil_scoped_acquire on invoke and destroy,
matching TelemetryRegistry::SetReportWarning, because apply_to uses
release_gil().

index_mapper rejects None (disable_none).

Tests

• Fail-before pyright/mypy on published stubs (reportArgumentType / arg-type).
• ./rdev.sh develop --stop-at robotpy-wpilib regenerated
  Callable[[int, int], int] at __init__.pyi line 10041.
• Runtime: map_index(None) TypeError; callback survives return and is
  invoked from apply_to; reverse remap completes without crash.

Does not retarget other SupportsInt callback stubs.

[auscompgeek]

1. I don't think this is the right place to fix this.
2. This lacks tests, and appears to be AI generated.