Struct.field_set - support setting subproperties (#92899)

Extend `Struct.field_set()` so that the `path` type can be a
`dna.FieldPath`, to mirror `Struct.field_get`'s `path` type, and allow
users to set file-block's subproperties. For example this allows
setting `object_block[(b'id', 'name')]`.

Also, along the way, added a test for getting subproperty value.

Reviewed-on: https://projects.blender.org/blender/blender-asset-tracer/pulls/92899

blender_asset_tracer/blendfile/__init__.py

@@ -726,7 +726,7 @@ class BlendFileBlock:
             hsh = zlib.adler32(str(value).encode(), hsh)
         return hsh
 
-    def set(self, path: bytes, value):
+    def set(self, path: dna.FieldPath, value):
         dna_struct = self.bfile.structs[self.sdna_index]
         self.bfile.mark_modified()
         self.bfile.fileobj.seek(self.file_offset, os.SEEK_SET)
@@ -835,7 +835,7 @@ class BlendFileBlock:
     def __getitem__(self, path: dna.FieldPath):
         return self.get(path)
 
-    def __setitem__(self, item: bytes, value) -> None:
+    def __setitem__(self, item: dna.FieldPath, value) -> None:
         self.set(item, value)
 
     def has_field(self, name: bytes) -> bool:

blender_asset_tracer/blendfile/dna.py

@@ -310,7 +310,7 @@ class Struct:
         self,
         file_header: header.BlendFileHeader,
         fileobj: typing.IO[bytes],
-        path: bytes,
+        path: FieldPath,
         value: typing.Any,
     ):
         """Write a value to the blend file.
@@ -319,7 +319,6 @@ class Struct:
         struct on disk (e.g. the start of the BlendFileBlock containing the
         data).
         """
-        assert isinstance(path, bytes), "path should be bytes, but is %s" % type(path)
 
         field, offset = self.field_from_path(file_header.pointer_size, path)