Address grill follow-ups: dead code, UUID filename, continuation guard, DataRateLimits

N1: Delete unused CodecSelector.selectEncoder. VideoCompressor calls
findEncoder directly; selectEncoder was dead since the initial commit.

N2: Switch Android output filename from System.currentTimeMillis() to
UUID.randomUUID(). Eliminates the collision risk when two compressions
start in the same millisecond.

N3: Guard CheckedContinuation against double-resume in both
processVideoTrack and processAudioTrack. AVAssetWriter shouldn't
re-invoke the requestMediaDataWhenReady block after markAsFinished, but
if it did, the previous code would crash via CheckedContinuation's
double-resume detection. Added a `finished` flag plus a local `finish`
closure that no-ops on second call.

N4: DataRateLimits window duration changed from Int `1` to Double `1.0`.
VideoToolbox expects the duration value as a CFNumber with float
semantics; Int bridges to NSNumber(int) which works on most iOS
versions but is not spec-correct.

modules/expo-bluesky-video-compress/ios/VideoCompressor.swift

@@ -113,7 +113,7 @@ class VideoCompressor {
     ]
     let peakBytesPerSecond = Int(Double(effectiveBitrate) / 8.0 * 1.5)
     compressionProps[kVTCompressionPropertyKey_DataRateLimits as String] = [
-      peakBytesPerSecond, 1
+      peakBytesPerSecond, 1.0
     ] as CFArray
 
     let videoColorProps: [String: Any] = [
@@ -259,20 +259,27 @@ class VideoCompressor {
   ) async {
     var lastProgressTime: CFAbsoluteTime = 0
     var lastAppendedPTS: CMTime?
+    var finished = false
 
     await withCheckedContinuation { (continuation: CheckedContinuation<Void, Never>) in
       writerInput.requestMediaDataWhenReady(
         on: DispatchQueue(label: "com.bsky.videocompress.video")
       ) {
-        while writerInput.isReadyForMoreMediaData {
-          if self.isCancelled {
+        let finish = {
+          if !finished {
+            finished = true
             writerInput.markAsFinished()
             continuation.resume()
+          }
+        }
+        while writerInput.isReadyForMoreMediaData {
+          if finished { return }
+          if self.isCancelled {
+            finish()
             return
           }
           guard let sampleBuffer = readerOutput.copyNextSampleBuffer() else {
-            writerInput.markAsFinished()
-            continuation.resume()
+            finish()
             return
           }
 
@@ -286,8 +293,7 @@ class VideoCompressor {
           lastAppendedPTS = pts
 
           if !writerInput.append(sampleBuffer) {
-            writerInput.markAsFinished()
-            continuation.resume()
+            finish()
             return
           }
 
@@ -306,24 +312,31 @@ class VideoCompressor {
     readerOutput: AVAssetReaderOutput,
     writerInput: AVAssetWriterInput
   ) async {
+    var finished = false
+
     await withCheckedContinuation { (continuation: CheckedContinuation<Void, Never>) in
       writerInput.requestMediaDataWhenReady(
         on: DispatchQueue(label: "com.bsky.videocompress.audio")
       ) {
-        while writerInput.isReadyForMoreMediaData {
-          if self.isCancelled {
+        let finish = {
+          if !finished {
+            finished = true
             writerInput.markAsFinished()
             continuation.resume()
+          }
+        }
+        while writerInput.isReadyForMoreMediaData {
+          if finished { return }
+          if self.isCancelled {
+            finish()
             return
           }
           guard let sampleBuffer = readerOutput.copyNextSampleBuffer() else {
-            writerInput.markAsFinished()
-            continuation.resume()
+            finish()
             return
           }
           if !writerInput.append(sampleBuffer) {
-            writerInput.markAsFinished()
-            continuation.resume()
+            finish()
             return
           }
         }