fix(core): respect positional-only parameters in FunctionTool

[fhgffy]

Why are these changes needed?

FunctionTool accepts annotated functions with positional-only parameters and generates their schemas, but calling them fails because every argument is passed as a keyword. For example, def scale(value: int, /, *, factor: int = 2) validates {"value": 3} and then raises TypeError instead of returning 6.

Bind positional-only values in signature order and pass the remaining values as keywords. Cancellation-token injection follows the same binding rules; synchronous executor cancellation keeps its existing behavior.

Eight new regression cases cover sync/async functions, defaults, mixed keyword-only parameters, partial, and positional-only cancellation tokens. All eight fail on the original implementation. The complete core suite passes with the fix: 234 passed. Scoped Ruff, mypy and Pyright checks and the core wheel build also pass. Validation used Windows and Python 3.12.2 with the relevant dependencies aligned to uv.lock; .NET checks were not run.

Related issue number

Fixes #8319

Checks

• Reviewed documentation impact; argument schemas and public signatures stay the same.
• Added regression tests corresponding to the change.
• All GitHub checks have passed (pending CI).