Add MPS demuxer and FFmpeg H.264 video decode

- MpsDemuxer parses MPEG-PS packs (0x1BA) into video (0x1E0-0x1EF) and
  audio (0x1BD) PES packets with PTS/DTS at the 90kHz clock.
- VideoDecoder decodes Annex-B H.264 via JavaCPP FFmpeg 8.1.2, splitting
  the stream into access units (one slice NAL per packet) so each send
  yields a frame.
- CLI 'decode' command dumps frame metadata (720x480 YUVJ420P).
- Validated against Batman Begins: 72 frames decoded.

core/build.gradle.kts

@@ -9,6 +9,9 @@ java {
 }
 
 dependencies {
+    api(libs.ffmpeg)
+    runtimeOnly("org.bytedeco:ffmpeg:${libs.versions.ffmpeg.get()}:linux-x86_64")
+
     testImplementation(platform(libs.junit.bom))
     testImplementation(libs.junit.jupiter)
     testRuntimeOnly(libs.junit.platform.launcher)