Add comprehensive test cases for cuddDecomp.c

[Copilot]

Adds test coverage for src/cuddDecomp.c BDD decomposition functions. Coverage improved from 59.17% to 67.69%.

Changes

• All 8 public decomposition APIs tested: GenConj/GenDisj, ApproxConj/ApproxDisj, IterConj/IterDisj, VarConj/VarDisj
• BDD structure variations: AND/OR chains, mixed patterns, XOR structures, ITE patterns, complemented edges
• Stress tests: Large BDDs (100+ vars), complex sharing patterns, multiple decomposition iterations
• Edge cases: Constants, single variables, zero cofactor paths, timeout handler registration

Coverage Limitation

90% target not achievable without memory allocation mocking:

• ~252 lines are CUDD_MEMORY_OUT error handlers
• ~74 lines are rare internal hash table state-dependent paths in CheckInTables, PickOnePair, PairInTables

Theoretical max without mocking: ~75%

Example Test Pattern

TEST_CASE("cuddDecomp - BuildConjuncts specific paths") {
    DdManager *manager = Cudd_Init(0, 0, CUDD_UNIQUE_SLOTS, CUDD_CACHE_SLOTS, 0);
    
    // Create BDD with Nv==zero structure to trigger ZeroCase path
    DdNode *notx0 = Cudd_Not(vars[0]);
    DdNode *f = Cudd_bddAnd(manager, notx0, complexExpr);
    Cudd_Ref(f);
    
    DdNode **conjuncts = nullptr;
    int result = Cudd_bddGenConjDecomp(manager, f, &conjuncts);
    REQUIRE(result >= 1);
    // cleanup...
}

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Original prompt

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

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