Add check_validity function and basic tests (Step 1 of Issue #988)

Hi everyone!✨🪐 This is step one from Issue #988 (closed)

Summary This MR implements Step 1 of Issue #988 (closed) by adding the new function:

pyxel/util/check_validity.py

The function provides generic runtime validation for typed parameters, supporting:

• standard Python types
• Annotated[…]
• annotated_types metadata (Ge, Gt, Le, Lt, Interval)
• Literal[…]
• tuple[…]
• Union / Optional

It raises TypeError for incorrect types and ValueError for invalid values, as required in the issue.

Tests Added: tests/util/test_check_validity_basic.py

Tests cover valid/invalid types, Annotated constraints, Literal, and tuple validation. Please see attached screenshot.

Scope This MR is self-contained and does not modify existing model behavior.
Further steps (ValueDescriptor integration, YAML validation, extended metadata) will follow in separate MRs.