git: add missing `repository.imanifestdict` methods to `gittreemanifest`

The next logical step was to explicitly subclass `repository.imanifestdict`, but
pytype flagged a few missing methods, because they're marked abstract.

    File "/mnt/c/Users/Matt/hg/hgext/git/manifest.py", line 238, in copy:
        Can't instantiate gittreemanifest with abstract methods dirs, fastdelta, set [not-instantiable]
    File "/mnt/c/Users/Matt/hg/hgext/git/manifest.py", line 287, in read:
        Can't instantiate gittreemanifest with abstract methods dirs, fastdelta, set [not-instantiable]
    File "/mnt/c/Users/Matt/hg/hgext/git/manifest.py", line 309, in read:
        Can't instantiate gittreemanifest with abstract methods dirs, fastdelta, set [not-instantiable]

I'm not bothering to figure out how to implement them- add them to appease
pytype, and put a TODO to fill in a proper implementation later.

hgext/git/manifest.py

@@ -4,6 +4,7 import typing
 
 from typing import (
     Any,
+    Iterable,
     Iterator,
     Set,
 )
@@ -117,6 +118,9 class gittreemanifest:
     def __iter__(self) -> Iterator[bytes]:
         return self.iterkeys()
 
+    def set(self, path: bytes, node: bytes, flags: bytes) -> None:
+        raise NotImplementedError  # TODO: implement this
+
     def __setitem__(self, path: bytes, node: bytes) -> None:
         self._pending_changes[path] = node, self.flags(path)
 
@@ -135,6 +139,9 class gittreemanifest:
     def _dirs(self):
         return pathutil.dirs(self)
 
+    def dirs(self) -> pathutil.dirs:
+        return self._dirs  # TODO: why is there a prpoertycache?
+
     def hasdir(self, dir: bytes) -> bool:
         return dir in self._dirs
 
@@ -258,6 +265,11 class gittreemanifest:
         # TODO can this method move out of the manifest iface?
         raise NotImplementedError
 
+    def fastdelta(
+        self, base: ByteString, changes: Iterable[tuple[bytes, bool]]
+    ) -> tuple[ByteString, ByteString]:
+        raise NotImplementedError  # TODO: implement this
+
     def _walkonetree(self, tree, match, subdir):
         for te in tree:
             # TODO: can we prune dir walks with the matcher?