Try marking ct_eq, conditional_select, conditional_negate with #[inline]

[divergentdave]

Reviewing recent changes to the subtle crate brought it to my attention that the ConstantTimeEq, ConditionallySelectable, and ConditionallyNegatable traits suggest using the #[inline] attribute on implementations of their methods. This is recommended for performance reasons, see dalek-cryptography/subtle@5a8d66c. We should try this out, particularly on shorter such methods, and see if it has a meaningful impact on benchmarks.