Add comprehensive type conversion tests for issue #961
- Add integer conversion tests (signed/unsigned, truncation, extension)
- Add float conversion tests (precision loss, special values, overflow)
- Add untyped constant conversion tests
- Add overflow and wrapping behavior tests
These tests cover the gaps identified in the code review:
1. Signed/unsigned conversions with negative values
2. Truncation from larger to smaller integer types
3. Sign extension vs zero extension
4. Float-to-int conversions with overflow/saturation
5. Int-to-float conversions with precision loss
6. Untyped constants with typed variables
7. Integer overflow and wrapping behavior
8. Special float values (Inf, NaN)
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Co-authored-by: cpunion <cpunion@users.noreply.github.com>
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