Consolidate stream classes into single module

- Move AttachmentStream and DataStream from separate modules into av/stream.py
- Convert stream.pyx from Cython to pure Python
- Add missing 'options' property to Stream type hints

This consolidation reduces code duplication and simplifies the module
structure without changing the public API.

Author: WyattBlue

av/attachments/__init__.py

@@ -3,8 +3,8 @@ from typing import Sequence, TypeVar, Union, overload
 
 from av.audio import _AudioCodecName
 from av.audio.stream import AudioStream
-from av.data.stream import DataStream
 from av.packet import Packet
+from av.stream import DataStream
 from av.subtitles.stream import SubtitleStream
 from av.video import _VideoCodecName
 from av.video.stream import VideoStream

av/attachments/stream.pxd

@@ -1,9 +1,7 @@
 from typing import Iterator, Literal, overload
 
-from av.attachments.stream import AttachmentStream
 from av.audio.stream import AudioStream
-from av.data.stream import DataStream
-from av.stream import Stream
+from av.stream import AttachmentStream, DataStream, Stream
 from av.subtitles.stream import SubtitleStream
 from av.video.stream import VideoStream