Add comprehensive tests for cuddSign.c achieving 86.5% coverage

[Copilot]

Added test cases for Cudd_CofMinterm function in src/cuddSign.c targeting 90% coverage. Achieved 86.5% line coverage (64/74 lines) and 100% function coverage.

Test Coverage

• Constant functions: DD_ONE, DD_ZERO with single variable
• Variable combinations: Single, two, and multi-variable (3-8 vars) functions
• Boolean operations: AND, OR, XOR compositions
• BDD structures: Complemented edges, shared nodes (ref > 1), ref=1 cleanup paths
• Edge cases: Skipped variable levels, ITE functions, ADD constants
• Recursion paths: Loop coverage in ddCofMintermAux, cache insertion paths

Uncovered Lines (13.5%)

The remaining 10 lines are memory allocation failure handlers:

• st_init_table failure (lines 119, 121-122)
• ALLOC failures (lines 142, 225-226)
• st_add_direct OOM (lines 276-277)

These require memory mocking infrastructure to test.

Example Test

TEST_CASE("Cudd_CofMinterm - Two variables", "[cuddSign]") {
    DdManager *manager = Cudd_Init(0, 0, CUDD_UNIQUE_SLOTS, CUDD_CACHE_SLOTS, 0);
    DdNode *x = Cudd_bddNewVar(manager);
    DdNode *y = Cudd_bddNewVar(manager);
    Cudd_Ref(x); Cudd_Ref(y);

    DdNode *f = Cudd_bddAnd(manager, x, y);
    Cudd_Ref(f);

    double *result = Cudd_CofMinterm(manager, f);
    REQUIRE(result[Cudd_ReadSize(manager)] == Catch::Approx(0.25)); // 1/4 minterms

    FREE(result);
    // cleanup...
}

Warning

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Original prompt

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

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