[performance] massively improved ActivityPub delivery worker efficiency (#2812)

* 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{}

internal/httpclient/sign.go

@@ -32,9 +32,7 @@ type SignFunc func(r *http.Request) error
 // (RoundTripper implementer) to check request
 // context for a signing function and using for
 // all subsequent trips through RoundTrip().
-type signingtransport struct {
-	http.Transport // underlying transport
-}
+type signingtransport struct{ http.Transport }
 
 func (t *signingtransport) RoundTrip(r *http.Request) (*http.Response, error) {
 	// Ensure updated host always set.