refactor(core): standardize HttpError

[iuioiua]

• Now extends Error, so that it satisfies instanceof Error operations.
• Narrows the status property to be an actual HTTP status code.
• Outsources default evaluation of the message property to @std/http/status, which already implements this functionality.
• Brings the stack property to the class, regardless of its status, which seems like a needless constraint.

[marvinhagemeister]

LGTM