feat: integrate multi-cloud storage (S3, OSS, COS, Local)

Add built-in storage support from v-hono-storage module:
- StorageProvider interface with 4 backends
- FileService with HTTP handlers
- Multipart upload support
- 86 property-based tests
- Retry mechanism with exponential backoff

Breaking: None (backward compatible)

storage_interface.v

@@ -0,0 +1,164 @@
+module hono
+
+import io
+
+// 存储操作结果
+pub struct StorageResult {
+pub:
+	success    bool
+	object_key string
+	etag       string
+	size       i64
+	error_msg  string
+}
+
+// 文件对象信息
+pub struct ObjectInfo {
+pub:
+	key           string
+	size          i64
+	etag          string
+	content_type  string
+	last_modified i64
+	metadata      map[string]string
+}
+
+// 列表选项
+pub struct ListOptions {
+pub:
+	prefix      string
+	delimiter   string
+	max_keys    int = 1000
+	start_after string
+}
+
+// 列表结果
+pub struct ListResult {
+pub:
+	objects         []ObjectInfo
+	common_prefixes []string
+	is_truncated    bool
+	next_marker     string
+}
+
+// 预签名URL选项
+pub struct PresignOptions {
+pub:
+	expires_in   int    = 3600 // 秒
+	method       string = 'GET'
+	content_type string
+}
+
+// 分片信息
+pub struct PartInfo {
+pub:
+	part_number int
+	etag        string
+	size        i64
+}
+
+
+// 统一存储接口
+pub interface StorageProvider {
+mut:
+	// 基本操作
+	upload(bucket string, key string, data []u8, content_type string) !StorageResult
+	upload_stream(bucket string, key string, mut reader io.Reader, size i64, content_type string) !StorageResult
+	download(bucket string, key string) ![]u8
+	download_stream(bucket string, key string, mut writer io.Writer) !i64
+	delete(bucket string, key string) !
+	exists(bucket string, key string) !bool
+	// 元数据操作
+	head(bucket string, key string) !ObjectInfo
+	copy(src_bucket string, src_key string, dst_bucket string, dst_key string) !StorageResult
+	// 列表操作
+	list(bucket string, options ListOptions) !ListResult
+	// 预签名URL
+	presign_url(bucket string, key string, options PresignOptions) !string
+	// 分片上传
+	init_multipart(bucket string, key string, content_type string) !string // 返回 upload_id
+	upload_part(bucket string, key string, upload_id string, part_number int, data []u8) !string // 返回 etag
+	complete_multipart(bucket string, key string, upload_id string, parts []PartInfo) !StorageResult
+	abort_multipart(bucket string, key string, upload_id string) !
+	// Bucket 操作
+	create_bucket(bucket string) !
+	delete_bucket(bucket string) !
+	bucket_exists(bucket string) !bool
+	// 获取提供者名称
+	provider_name() string
+}
+
+// 创建成功的存储结果
+pub fn new_storage_result(object_key string, etag string, size i64) StorageResult {
+	return StorageResult{
+		success: true
+		object_key: object_key
+		etag: etag
+		size: size
+		error_msg: ''
+	}
+}
+
+// 创建失败的存储结果
+pub fn new_storage_error_result(error_msg string) StorageResult {
+	return StorageResult{
+		success: false
+		object_key: ''
+		etag: ''
+		size: 0
+		error_msg: error_msg
+	}
+}
+
+// 创建对象信息
+pub fn new_object_info(key string, size i64, etag string, content_type string, last_modified i64) ObjectInfo {
+	return ObjectInfo{
+		key: key
+		size: size
+		etag: etag
+		content_type: content_type
+		last_modified: last_modified
+		metadata: map[string]string{}
+	}
+}
+
+// 创建带元数据的对象信息
+pub fn new_object_info_with_metadata(key string, size i64, etag string, content_type string, last_modified i64, metadata map[string]string) ObjectInfo {
+	return ObjectInfo{
+		key: key
+		size: size
+		etag: etag
+		content_type: content_type
+		last_modified: last_modified
+		metadata: metadata
+	}
+}
+
+// 创建空的列表结果
+pub fn new_empty_list_result() ListResult {
+	return ListResult{
+		objects: []ObjectInfo{}
+		common_prefixes: []string{}
+		is_truncated: false
+		next_marker: ''
+	}
+}
+
+// 创建列表结果
+pub fn new_list_result(objects []ObjectInfo, common_prefixes []string, is_truncated bool, next_marker string) ListResult {
+	return ListResult{
+		objects: objects
+		common_prefixes: common_prefixes
+		is_truncated: is_truncated
+		next_marker: next_marker
+	}
+}
+
+// 创建分片信息
+pub fn new_part_info(part_number int, etag string, size i64) PartInfo {
+	return PartInfo{
+		part_number: part_number
+		etag: etag
+		size: size
+	}
+}