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_test.go

@@ -0,0 +1,50 @@
+// 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 (
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"testing"
+
+	"github.com/infinite-iroha/touka"
+)
+
+func TestRegister(t *testing.T) {
+	r := touka.New()
+	cfg := &Config{
+		FileSystem: NewMemFS(),
+	}
+	Register(r, "/dav", cfg)
+
+	// Check if a WebDAV method is registered
+	req, _ := http.NewRequest("PROPFIND", "/dav/", nil)
+	w := httptest.NewRecorder()
+	r.ServeHTTP(w, req)
+
+	if w.Code == http.StatusNotFound {
+		t.Errorf("Expected PROPFIND to be registered, but got 404")
+	}
+}
+
+func TestServe(t *testing.T) {
+	r := touka.New()
+	dir, _ := os.MkdirTemp("", "webdav")
+	defer os.RemoveAll(dir)
+
+	if err := Serve(r, "/serve", dir); err != nil {
+		t.Fatalf("Serve failed: %v", err)
+	}
+
+	// Check if a WebDAV method is registered
+	req, _ := http.NewRequest("OPTIONS", "/serve/", nil)
+	w := httptest.NewRecorder()
+	r.ServeHTTP(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Errorf("Expected OPTIONS to return 200, but got %d", w.Code)
+	}
+}