Increase metadata coverage for `speced/fn`

[vemv]

Problem statement

speced/fn lacks specific coverage for metadata (type hint) emission. Its coverage is only concerned with :pre/:post emission.

Note that the implementation is shared with that of defn, which is fully covered, so it's nearly impossible that the shared code does not work for the fn case.

The difficulty lies in that one cannot access fn metadata.

Proposal

Inspect the speced/fn macroexpansions, verifying its contained metadata.

Alternatives and comparison

• Do nothing
  • As mentioned, it can be acceptable, but I'd rather keep things proven.