feat: Add support for custom MP4 metadata with mdta format (#132)

* feat: Add support for custom MP4 metadata with mdta format

- Add metadataFormat option ('mdir' | 'mdta') to IsobmffOutputFormatOptions
- Implement complete mdta format with keys box generation
- Enable custom metadata fields readable by ffmpeg/ffprobe
- Maintain backward compatibility with default mdir format

* Refactor ISOBMFF metadata tag writing logic

* Autism

---------

Co-authored-by: tanfu <[email protected]>
Co-authored-by: Vanilagy <[email protected]>

dev/demux.html

@@ -14,6 +14,10 @@
 			source: new Mediabunny.BlobSource(file),
 		});
 
+		console.log(await input.getMetadataTags());
+
+		/*
+
 		const videoTrack = await input.getPrimaryVideoTrack();
 		const sink = new Mediabunny.VideoSampleSink(videoTrack);
 		const sink2 = new Mediabunny.EncodedPacketSink(videoTrack);
@@ -37,6 +41,7 @@
 				break;
 			}
 		}
+		*/
 
 		/*
 		const sink = new Mediabunny.EncodedPacketSink(videoTrack);