fix: Add watchOS to AVAssetDownloadTask availability check

[KYHyeon]

Summary

Fix build failures on tvOS and watchOS platforms caused by AVAssetDownloadTask unavailability.

Problem

The recent upstream commit (6dff47c) added a check to filter out AVAssetDownloadTask to prevent crashes during
swizzling. However, AVAssetDownloadTask is only available on iOS and macOS, causing compilation errors on tvOS and
watchOS:

❌ 'AVAssetDownloadTask' is unavailable in tvOS
❌ 'AVAssetDownloadTask' is unavailable in watchOS

Solution

Added platform-specific conditional compilation to exclude the AVAssetDownloadTask check on tvOS and watchOS:

#if !os(tvOS) && !os(watchOS)
    guard !task.isKind(of: AVAssetDownloadTask.self) else { return }
#endif

Why This Is Safe

1. tvOS/watchOS: AVAssetDownloadTask doesn't exist on these platforms, so no such tasks will ever be created. The
check can be safely skipped.
2. iOS/macOS: The check remains in place to prevent crashes when encountering AVAssetDownloadTask instances (used
for HLS streaming).

Testing

- ✅ Builds successfully on all platforms (iOS, tvOS, watchOS, macOS)
- ✅ No functional changes for iOS/macOS
- ✅ Fixes compilation errors on tvOS/watchOS

Related Issues

- Fixes build failures in CI/CD pipelines for tvOS and watchOS targets
- Maintains compatibility with the upstream fix for AVAssetDownloadTask crash (commit 6dff47cd)

[kean]

Thank you!