[security] transport.Controller{} and transport.Transport{} security and performance improvements (#564)

* cache transports in controller by privkey-generated pubkey, add retry logic to transport requests

Signed-off-by: kim <grufwub@gmail.com>

* update code comments, defer mutex unlocks

Signed-off-by: kim <grufwub@gmail.com>

* add count to 'performing request' log message

Signed-off-by: kim <grufwub@gmail.com>

* reduce repeated conversions of same url.URL object

Signed-off-by: kim <grufwub@gmail.com>

* move worker.Worker to concurrency subpackage, add WorkQueue type, limit transport http client use by WorkQueue

Signed-off-by: kim <grufwub@gmail.com>

* fix security advisories regarding max outgoing conns, max rsp body size

- implemented by a new httpclient.Client{} that wraps an underlying
  client with a queue to limit connections, and limit reader wrapping
  a response body with a configured maximum size
- update pub.HttpClient args passed around to be this new httpclient.Client{}

Signed-off-by: kim <grufwub@gmail.com>

* add httpclient tests, move ip validation to separate package + change mechanism

Signed-off-by: kim <grufwub@gmail.com>

* fix merge conflicts

Signed-off-by: kim <grufwub@gmail.com>

* use singular mutex in transport rather than separate signer mus

Signed-off-by: kim <grufwub@gmail.com>

* improved useragent string

Signed-off-by: kim <grufwub@gmail.com>

* add note regarding missing test

Signed-off-by: kim <grufwub@gmail.com>

* remove useragent field from transport (instead store in controller)

Signed-off-by: kim <grufwub@gmail.com>

* shutup linter

Signed-off-by: kim <grufwub@gmail.com>

* reset other signing headers on each loop iteration

Signed-off-by: kim <grufwub@gmail.com>

* respect request ctx during retry-backoff sleep period

Signed-off-by: kim <grufwub@gmail.com>

* use external pkg with docs explaining performance "hack"

Signed-off-by: kim <grufwub@gmail.com>

* use http package constants instead of string method literals

Signed-off-by: kim <grufwub@gmail.com>

* add license file headers

Signed-off-by: kim <grufwub@gmail.com>

* update code comment to match new func names

Signed-off-by: kim <grufwub@gmail.com>

* updates to user-agent string

Signed-off-by: kim <grufwub@gmail.com>

* update signed testrig models to fit with new transport logic (instead uses separate signer now)

Signed-off-by: kim <grufwub@gmail.com>

* fuck you linter

Signed-off-by: kim <grufwub@gmail.com>

internal/processing/processor_test.go

@@ -29,6 +29,7 @@ import (
 	"codeberg.org/gruf/go-store/kv"
 	"github.com/stretchr/testify/suite"
 	"github.com/superseriousbusiness/activity/streams"
+	"github.com/superseriousbusiness/gotosocial/internal/concurrency"
 	"github.com/superseriousbusiness/gotosocial/internal/db"
 	"github.com/superseriousbusiness/gotosocial/internal/email"
 	"github.com/superseriousbusiness/gotosocial/internal/federation"
@@ -40,7 +41,6 @@ import (
 	"github.com/superseriousbusiness/gotosocial/internal/timeline"
 	"github.com/superseriousbusiness/gotosocial/internal/transport"
 	"github.com/superseriousbusiness/gotosocial/internal/typeutils"
-	"github.com/superseriousbusiness/gotosocial/internal/worker"
 	"github.com/superseriousbusiness/gotosocial/testrig"
 )
 
@@ -217,8 +217,8 @@ func (suite *ProcessingStandardTestSuite) SetupTest() {
 		}, nil
 	})
 
-	clientWorker := worker.New[messages.FromClientAPI](-1, -1)
-	fedWorker := worker.New[messages.FromFederator](-1, -1)
+	clientWorker := concurrency.NewWorkerPool[messages.FromClientAPI](-1, -1)
+	fedWorker := concurrency.NewWorkerPool[messages.FromFederator](-1, -1)
 
 	suite.transportController = testrig.NewTestTransportController(httpClient, suite.db, fedWorker)
 	suite.mediaManager = testrig.NewTestMediaManager(suite.db, suite.storage)