Add f16 and f128 test cases to manual_float_methods

[slightsharp]

This PR adds test cases for f16 and f128 types to the manual_float_methods test suite. While the lint doesn't currently detect these patterns (which is expected since f16/f128 support may need to be implemented), these test cases serve as:

1. Documentation of the expected behavior
2. Preparation for future f16/f128 support
3. Regression prevention

The test cases include both manual_is_infinite and manual_is_finite patterns for both f16 and f128 types, with the necessary feature flags enabled.

changelog: none

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