feat: recoverer middleware

[davidspiess]

Introduces a recoverer middleware that handles panics and delegates error response handling to the caller.

Two tests are included: one with a plain text error response and another with a structured JSON response.
It should also work with a dedicated library like ory/herodot.

[francesconi]

I wouldn't unit test different error handlers but instead ensure that http.ErrAbortHandler is not recovered. Also, do we want to add a default error handler, or should we enforce that the user always sets one?

[francesconi]

LGTM