[feature] add worker task serialization logic (#2989)

* improved server shutdown with more precise shutdown of modules + deferring of ALL of it

* move delivery and workers into separate files

* add worker task model and Serialize() / Deserialize() methods for message types

* start adding message serialize / deserialize tests

* start adding test cases

* update body rewinding to rely on standard library mechanism of r.GetBody()

* remove request rewinding (http.Client{} should already handle this)

* standard library already handles rewinding

* improved code comment

* move the newPOST() function contents to prepare(), fits better with current API

* add Serialize() / Deserialize() implementations for Delivery{} type

* finish writing FromClientAPI sserialize / deserialize tests

* start adding FromFediAPI{} serialize / deserialize test cases

* fix FromFediAPI{} tests

* add tests for delivery message type

* fix repeat code

* missing license header

* use testrig status and accounts for marshal / unmarshaling tests

* add a specific test for checking account RSA keys are preserved

internal/gtsmodel/workertask.go

@@ -0,0 +1,41 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package gtsmodel
+
+import "time"
+
+type WorkerType uint8
+
+const (
+	DeliveryWorker  WorkerType = 1
+	FederatorWorker WorkerType = 2
+	ClientWorker    WorkerType = 3
+)
+
+// WorkerTask represents a queued worker task
+// that was persisted to the database on shutdown.
+// This is only ever used on startup to pickup
+// where we left off, and on shutdown to prevent
+// queued tasks from being lost. It is simply a
+// means to store a blob of serialized task data.
+type WorkerTask struct {
+	ID         uint      `bun:""`
+	WorkerType uint8     `bun:""`
+	TaskData   []byte    `bun:""`
+	CreatedAt  time.Time `bun:""`
+}