This PR makes `@[cbv_opaque]` unconditionally block all evaluation of a
constant
by `cbv`, including `@[cbv_eval]` rewrite rules. Previously,
`@[cbv_eval]` could
bypass `@[cbv_opaque]`, and for bare constants (not applications),
`isOpaqueConst`
could fall through to `handleConst` which would unfold the definition
body.
The intended usage pattern is now: mark subterm-producing functions
(like
`DHashMap.insert`) as `@[cbv_opaque]` to prevent unfolding, and provide
`@[cbv_eval]` theorems on the *consuming* function (like
`DHashMap.contains`)
which pattern-matches against the opaque subterms.
de2b177423