fix(IRouter): return types

[didinele]

IRouter methods used to return T, but this is incorrect. An IRouter implementation will never be sync, this is HTTP we're talking about.

[zaida04]

A general thing, shouldn’t it be Promise<T | unknown>? In the event that the end user does not pass in a generic? Anyways I’ll approve the changes in the event I’m mistaken.

[didinele]

A general thing, shouldn’t it be Promise<T | unknown>? In the event that the end user does not pass in a generic? Anyways I’ll approve the changes in the event I’m mistaken.

T | unknown is incorrect, if the user passes number or.. anything into T TS resolves that union into unknown, meaning that the user's generic becomes irrelevant. When the user does not pass anything TS does actually yield Promise<unknown>