feat: add native WebDAV submodule and usability helpers

This commit introduces a new, high-performance, and extensible WebDAV submodule, implemented natively without external dependencies. It also adds a high-level API to simplify common use cases.

The submodule includes:
- A core WebDAV handler that supports essential methods: PROPFIND, MKCOL, GET, PUT, DELETE, COPY, MOVE, LOCK, and UNLOCK.
- An extensible design using a `FileSystem` interface to decouple the protocol logic from the storage backend.
- Two `FileSystem` implementations:
  - `MemFS`: An in-memory, tree-based filesystem for testing and ephemeral storage.
  - `OSFS`: A secure, OS-based filesystem that interacts with the local disk, including robust path traversal and symlink protection.
- A `LockSystem` interface with an in-memory implementation (`MemLock`) that supports resource locking and includes a graceful shutdown mechanism.
- A high-level API in `webdav/easy.go` (`Serve`, `Register`) to simplify serving local directories.
- RFC 4918 compliance for core operations.
- Performance optimizations, including `sync.Pool` for object reuse and `sync/atomic` for lock-free field access.
- Comprehensive unit tests and a working example application.

The Touka framework's core has been updated to recognize all WebDAV-specific HTTP methods. This implementation addresses numerous points from detailed code reviews, including security vulnerabilities, memory leaks, RFC compliance issues, and path handling bugs.

webdav/easy.go

@@ -0,0 +1,48 @@
+// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+// Copyright 2024 WJQSERVER. All rights reserved.
+// All rights reserved by WJQSERVER, related rights can be exercised by the infinite-iroha organization.
+package webdav
+
+import (
+	"log"
+	"os"
+
+	"github.com/infinite-iroha/touka"
+)
+
+// Config is a configuration for the WebDAV handler.
+type Config struct {
+	FileSystem FileSystem
+	LockSystem LockSystem
+	Logger     Logger
+}
+
+// Register registers a WebDAV handler on the given router.
+func Register(engine *touka.Engine, prefix string, cfg *Config) {
+	if cfg.LockSystem == nil {
+		cfg.LockSystem = NewMemLock()
+	}
+
+	handler := NewHandler(prefix, cfg.FileSystem, cfg.LockSystem, cfg.Logger)
+
+	webdavMethods := []string{
+		"OPTIONS", "GET", "HEAD", "DELETE", "PUT", "MKCOL", "COPY", "MOVE", "PROPFIND", "PROPPATCH", "LOCK", "UNLOCK",
+	}
+	engine.HandleFunc(webdavMethods, prefix+"/*path", handler.ServeTouka)
+}
+
+// Serve serves a local directory via WebDAV.
+func Serve(engine *touka.Engine, prefix string, rootDir string) error {
+	fs, err := NewOSFS(rootDir)
+	if err != nil {
+		return err
+	}
+
+	cfg := &Config{
+		FileSystem: fs,
+		Logger:     log.New(os.Stdout, "", 0),
+	}
+	Register(engine, prefix, cfg)
+	return nil
+}