Replace queue v2 part2 (#58)

* Use simple intrusive linked list for queue

Use a simple intrusive list for the event queue.  The ultimate goal here
is to arrange that certain kinds of events (errors) can be guaranteed
to be queued, as client objects will leak if they are discarded.  As a
secondary improvement, there are some operations (peeking, remove_if)
that can be more efficient as we can hold the queue lock for longer.

This commit is a straight replacement and does not attempt any logic
changes.

* Factor common binding code

* Purge queue when unbinding

* _tcp_bind_api: Close automatically on failure

This eliminates a round-trip through the LwIP lock and allows
_tcp_close_api to specialize for AsyncClient.

* Complete AsyncClient close on LwIP thread

Ensure that _tcp_close completely disconnects a pcb from an AsyncClient
- All callbacks are unhooked
- All events are purged
- abort() called on close() failure
This fixes some race conditions with closing, particularly without
CONFIG_LWIP_TCPIP_CORE_LOCKING, where an event might be processed for a
now-dead client if it arrived after arg was cleared but before the
callbacks were disconnected.

* Add size cache to SimpleIntrusiveList

Cache the list length to avoid performing expensive lookups during
stochastic poll coaelescence.  This can be removed later when the
size() function is no longer necessary outside of a debug context.

* Remove singleton pattern on queue mutex

The creation check in the hot path comes at a
measurable performance cost.

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Co-authored-by: Mathieu Carbou <[email protected]>

Author: willmmiles