Fix connection port validation

[MuhammadMaazA]

Closes #68382

Connection port validation was inconsistent across model construction, JSON deserialization, the Task SDK, and the public API schema.

This change validates ports as integers in the inclusive 0..65535 range, preserves numeric JSON strings and empty ports, serializes port 0, and adds focused boundary coverage.

Tests:

• python -m py_compile on changed source and test files
• git diff --check

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