feat: add clipbin-media for reading segments with FFmpeg

One shared FFmpeg binding (ffmpeg-next 9, dynamically linked: the system
FFmpeg on Linux, the OBS-bundled DLLs on Windows) for clip export and
playback, with a probe of segment duration, codec, size and audio tracks.

Cargo.toml

@@ -2,6 +2,7 @@
 members = [
     "crates/clipbin-core",
     "crates/clipbin-desktop",
+    "crates/clipbin-media",
     "crates/clipbin-obs",
     "crates/clipbin-probe",
     "crates/rig-pointer",
@@ -19,6 +20,7 @@ publish = false
 
 [workspace.dependencies]
 clipbin-core = { path = "crates/clipbin-core" }
+clipbin-media = { path = "crates/clipbin-media" }
 clipbin-obs = { path = "crates/clipbin-obs" }
 gpui = "=0.2.2"
 # The tested OBS set: the libobs crate's bundled headers are OBS 32.0.4, matching