fix: handle ternary expressions in state variable initializers

[ep0chzer0]

Summary

• Fixes [Bug-Candidate]: The ternary operator does not support structs. #2836 - SlithIRError: Ternary operator are not convertible to SlithIR when ternary expressions are used in state variable initializers
• Root cause: State variable initializers are processed via synthetic CONSTRUCTOR_VARIABLES functions created in add_constructor_variables(), which runs after the normal function parsing pipeline. These synthetic functions never go through _rewrite_ternary_as_if_else(), so ConditionalExpression nodes reach SlithIR conversion unsplit
• Fix: Added _rewrite_ternary_in_constructor_variables() to Contract that performs the equivalent IF/EXPRESSION/ENDIF node splitting for constructor variable nodes, called after all nodes are created in add_constructor_variables()

Reproduction case (from issue)

contract A {
    struct S {
        uint32 user;
    }
}

contract B {
    A.S a;
    A.S b;
    uint32 result = (true ? a.user : b.user);
}

Before this fix, analyzing contract B would crash with:

SlithIRError: Ternary operator are not convertible to SlithIR if true then a.user else b.user

Test plan

• New unit test test_ternary_in_state_variable_initializer verifies parsing succeeds
• All existing CI checks pass

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