[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/federation/federatingactor_test.go

@@ -21,6 +21,7 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
+	"io"
 	"net/url"
 	"testing"
 	"time"
@@ -129,23 +130,27 @@ func (suite *FederatingActorTestSuite) TestSendRemoteFollower() {
 	suite.NotNil(activity)
 
 	// because we added 1 remote follower for zork, there should be a url in sentMessage
-	var sent [][]byte
+	var sent []byte
 	if !testrig.WaitFor(func() bool {
-		sentI, ok := httpClient.SentMessages.Load(*testRemoteAccount.SharedInboxURI)
-		if ok {
-			sent, ok = sentI.([][]byte)
-			if !ok {
-				panic("SentMessages entry was not []byte")
-			}
-			return true
+		delivery, ok := suite.state.Workers.Delivery.Queue.Pop()
+		if !ok {
+			return false
 		}
-		return false
+		if !testrig.EqualRequestURIs(delivery.Request.URL, *testRemoteAccount.SharedInboxURI) {
+			panic("differing request uris")
+		}
+		sent, err = io.ReadAll(delivery.Request.Body)
+		if err != nil {
+			panic("error reading body: " + err.Error())
+		}
+		return true
+
 	}) {
 		suite.FailNow("timed out waiting for message")
 	}
 
 	dst := new(bytes.Buffer)
-	err = json.Indent(dst, sent[0], "", "  ")
+	err = json.Indent(dst, sent, "", "  ")
 	suite.NoError(err)
 	suite.Equal(`{
   "@context": "https://www.w3.org/ns/activitystreams",