[New Feature] Support SAM 2.1 (#59)

* support sam 2.1

* refine config path and ckpt path

* update README

demo/backend/server/inference/multipart.py

@@ -0,0 +1,48 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+# This source code is licensed under the license found in the
+# LICENSE file in the root directory of this source tree.
+
+from typing import Dict, Union
+
+
+class MultipartResponseBuilder:
+    message: bytes
+
+    def __init__(self, boundary: str) -> None:
+        self.message = b"--" + boundary.encode("utf-8") + b"\r\n"
+
+    @classmethod
+    def build(
+        cls, boundary: str, headers: Dict[str, str], body: Union[str, bytes]
+    ) -> "MultipartResponseBuilder":
+        builder = cls(boundary=boundary)
+        for k, v in headers.items():
+            builder.__append_header(key=k, value=v)
+        if isinstance(body, bytes):
+            builder.__append_body(body)
+        elif isinstance(body, str):
+            builder.__append_body(body.encode("utf-8"))
+        else:
+            raise ValueError(
+                f"body needs to be of type bytes or str but got {type(body)}"
+            )
+
+        return builder
+
+    def get_message(self) -> bytes:
+        return self.message
+
+    def __append_header(self, key: str, value: str) -> "MultipartResponseBuilder":
+        self.message += key.encode("utf-8") + b": " + value.encode("utf-8") + b"\r\n"
+        return self
+
+    def __close_header(self) -> "MultipartResponseBuilder":
+        self.message += b"\r\n"
+        return self
+
+    def __append_body(self, body: bytes) -> "MultipartResponseBuilder":
+        self.__append_header(key="Content-Length", value=str(len(body)))
+        self.__close_header()
+        self.message += body
+        return self