Disable automatic symmetry in proofs of theory explanations (#7493)

Disable automatic symmetry in proofs of theory explanations (#7493)

This avoids cyclic proofs in a rare case where theory explanations involve an equality and its symmetric form.

This PR disables auto-symmetry on lazy proofs used for theory explanations, which is slightly less convenient but avoids potentials for cyclic proofs. Note this complication would not arise if the theory engine did not allow non-rewritten equalities to be propagated between theories.

Fixes cvc5/cvc5-projects#311.