feat: add max3 utility

[DavePearce]

This adds the max3 utility for testing purposes

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Note

Adds max3_u128 zkasm function to compute the max of three u128 values and integrates it into the test suite with extensive test vectors.

• Assembly Utility:
  • Adds testdata/asm/util/max3.zkasm implementing max3_u128(arg1, arg2, arg3) -> res to return the maximum of three u128 values.
• Testing:
  • Introduces Test_AsmUtil_Max3 in pkg/test/assembly_util_test.go to run asm/util/max3 across fields.
  • Adds comprehensive accept vectors in testdata/asm/util/max3.accepts.

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