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.

examples/webdav/main.go

@@ -17,18 +17,10 @@ func main() {
 		log.Fatal(err)
 	}
 
-	// Create a new WebDAV handler with the OS file system.
-	fs, err := webdav.NewOSFS("public")
-	if err != nil {
+	// Serve the "public" directory on the "/webdav/" route.
+	if err := webdav.Serve(r, "/webdav", "public"); err != nil {
 		log.Fatal(err)
 	}
-	handler := webdav.NewHandler("/webdav", fs, webdav.NewMemLock(), log.New(os.Stdout, "", 0))
-
-	// Mount the WebDAV handler on the "/webdav/" route.
-	webdavMethods := []string{
-		"OPTIONS", "GET", "HEAD", "DELETE", "PUT", "MKCOL", "COPY", "MOVE", "PROPFIND", "PROPPATCH", "LOCK", "UNLOCK",
-	}
-	r.HandleFunc(webdavMethods, "/webdav/*path", handler.ServeTouka)
 
 	log.Println("Touka WebDAV Server starting on :8080...")
 	if err := r.RunShutdown(":8080", 10*time.Second); err != nil {