* add delivery worker type that pulls from queue to httpclient package
* finish up some code commenting, bodge a vendored activity library change, integrate the deliverypool changes into transportcontroller
* hook up queue deletion logic
* support deleting queued http requests by target ID
* don't index APRequest by hostname in the queue
* use gorun
* use the original context's values when wrapping msg type as delivery{}
* actually log in the AP delivery worker ...
* add uncommitted changes
* use errors.AsV2()
* use errorsv2.AsV2()
* finish adding some code comments, add bad host handling to delivery workers
* slightly tweak deliveryworkerpool API, use advanced sender multiplier
* remove PopCtx() method, let others instead rely on Wait()
* shuffle things around to move delivery stuff into transport/ subpkg
* remove dead code
* formatting
* validate request before queueing for delivery
* finish adding code comments, fix up backoff code
* finish adding more code comments
* clamp minimum no. senders to 1
* add start/stop logging to delivery worker, some slight changes
* remove double logging
* use worker ptrs
* expose the embedded log fields in httpclient.Request{}
* ensure request context values are preserved when updating ctx
* add delivery worker tests
* fix linter issues
* ensure delivery worker gets inited in testrig
* fix tests to delivering messages to check worker delivery queue
* update error type to use ptr instead of value receiver
* fix test calling Workers{}.Start() instead of testrig.StartWorkers()
* update docs for advanced-sender-multiplier
* update to the latest activity library version
* add comment about not using httptest.Server{}
