Add GetSignedType and GetUnsignedType

[Ivka-F]

This PR upstreams two new type utility functions from the jank-lang/CppInterOp fork,
originally authored by @jeaye.

• GetSignedType — returns the signed counterpart of an integral type (e.g. unsigned int -> int). Returns the type unchanged if it has no signed counterpart.
• GetUnsignedType — returns the unsigned counterpart of an integral type (e.g. int -> unsigned int). Returns the type unchanged if it has no unsigned counterpart.

Both functions follow the existing API conventions (INTEROP_TRACE, INTEROP_RETURN, null checks) and include unit tests in TypeReflectionTest.cpp covering all integral type cases including __int128.

These are purely additive — no existing behavior is changed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.06%. Comparing base (ed3696d) to head (653a6bb).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1010      +/-   ##
==========================================
+ Coverage   85.89%   86.06%   +0.16%     
==========================================
  Files          15       15              
  Lines        4971     5031      +60     
==========================================
+ Hits         4270     4330      +60     
  Misses        701      701              

Files with missing lines	Coverage Δ
lib/CppInterOp/CppInterOp.cpp	89.56% <100.00%> (+0.23%)	⬆️

Files with missing lines	Coverage Δ
lib/CppInterOp/CppInterOp.cpp	89.56% <100.00%> (+0.23%)	⬆️

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[Vipul-Cariappa]

LGTM!

[Vipul-Cariappa]

Can you please fix the Ubuntu CI failures? You may want to use macros for the LLVM version, and if CppInterOp is built with Cling.