Add comprehensive test cases for cuddAddWalsh.c

[Copilot]

Adds test coverage for Cudd_addWalsh and Cudd_addResidue functions. Achieves 64.8% line coverage and 100% function coverage.

Test Cases Added

Cudd_addWalsh:

• Base case (n=0), n=1 through n=4 exercising loop iterations
• Walsh matrix property verification (±1 terminals only)
• Memory management and stress tests

Cudd_addResidue:

• All option combinations: LSB/MSB, unsigned/two's complement
• Various moduli including primes
• Edge cases: n=1, different top variable indices
• Invalid parameter handling

Coverage Limitations

The remaining 35% (51 lines) consists entirely of error handling paths for:

• Memory allocation failures (ALLOC returning NULL)
• Internal function failures (cuddUniqueConst, cuddUniqueInter, Cudd_addIte)
• Timeout handler callback

These paths require mocking infrastructure to trigger—not achievable through normal unit testing without library modifications.

Example Test

TEST_CASE("Cudd_addWalsh - n=2 case with loop", "[cuddAddWalsh]") {
    DdManager *manager = Cudd_Init(0, 0, CUDD_UNIQUE_SLOTS, CUDD_CACHE_SLOTS, 0);
    
    DdNode *x[2], *y[2];
    for (int i = 0; i < 2; i++) {
        x[i] = Cudd_addIthVar(manager, i);
        y[i] = Cudd_addIthVar(manager, i + 2);
        Cudd_Ref(x[i]);
        Cudd_Ref(y[i]);
    }
    
    DdNode *result = Cudd_addWalsh(manager, x, y, 2);
    REQUIRE(result != nullptr);
    REQUIRE(Cudd_CountLeaves(result) == 2);  // Only +1 and -1
    
    // cleanup...
}

Warning

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If you need me to access, download, or install something from one of these locations, you can either:

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Original prompt

Complete test cases for src/cuddAddWalsh.c and target 90% coverage for the source file.

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