feat: retrieve routers from composable routers

[ajnavarro]

This is useful when you want to access specific features or metrics needed per router, like get DHT stats.

Signed-off-by: Antonio Navarro antnavper@gmail.com

[lidel]

sgtm as a quick way to unblock ipfs/kubo#9482, feel free to merge after addressing small asks in comments inline.

ps . (not a blocker, could be future PR) I wonder if it is I think it may be also useful to have separate funcs below (but can be future PR), which allows reading wrapper router attribites like things like Timeout or ExecureAfter

func (r *composableParallel) ParallelRouters() []*ParallelRouter {
  return r.routers
}
func (r *composableSequential) SequentialRouters() []*SequentialRouter {
  return r.routers
}