chore: fix 8.18 warnings · HoTT/Coq-HoTT@6523c89

succunary is declared opaque (Qed) but this is not fully respected

unarybinary is declared opaque (Qed) but this is not fully respected

binaryunary is declared opaque (Qed) but this is not fully respected

f_preserves_0 is declared opaque (Qed) but this is not fully

f_preserves_1 is declared opaque (Qed) but this is not fully

f_preserves_plus is declared opaque (Qed) but this is not fully

f_preserves_mult is declared opaque (Qed) but this is not fully

ineq_bzero_double1 is declared opaque (Qed) but this is not fully

ineq_bzero_double2 is declared opaque (Qed) but this is not fully

ineq_double1_double2 is declared opaque (Qed) but this is not fully

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