fix: Enable E2EE for VP9 codec (#953)

### Problem
While using the Flutter SDK with JS SDK and with E2EE enabled, the video
from Web can not be decrypted by the Flutter app.

## Summary
Enables end-to-end encryption (E2EE) for VP9 codec. Previously, E2EE was
skipped for all SVC codecs. This aligns the Flutter SDK with the JS SDK,
where E2EE works with VP9 codec.

## Changes
Removed `isSVCCodec()` and use `isAV1Codec()` to enable E2EE setup for
VP9 codec in `LocalTrackPublishedEvent` handler
Removed `isSVCCodec()` and use `isAV1Codec()` to enable E2EE setup for
VP9 codec in `TrackSubscribedEvent` handler

Is there any specific reason why E2EE is disabled for SVC codecs? 
I tried VP9 with this patch and the VP9 video from Web can be decrypted
by Flutter app.

Author: Linquas

lib/src/e2ee/e2ee_manager.dart

@@ -47,7 +47,7 @@ class E2EEManager {
       _listener!
         ..on<LocalTrackPublishedEvent>((event) async {
           if (event.publication.encryptionType == EncryptionType.kNone ||
-              isSVCCodec(event.publication.track?.codec ?? '')) {
+              isAV1Codec(event.publication.track?.codec ?? '')) {
             // no need to setup frame cryptor
             return;
           }
@@ -81,7 +81,7 @@ class E2EEManager {
         })
         ..on<TrackSubscribedEvent>((event) async {
           final codec = event.publication.mimeType.split('/')[1];
-          if (event.publication.encryptionType == EncryptionType.kNone || isSVCCodec(codec)) {
+          if (event.publication.encryptionType == EncryptionType.kNone || isAV1Codec(codec)) {
             // no need to setup frame cryptor
             return;
           }

lib/src/utils.dart

@@ -567,6 +567,8 @@ const refreshSubscribedCodecAfterNewCodec = 5000;
 
 bool isSVCCodec(String codec) => ['vp9', 'av1'].contains(codec.toLowerCase());
 
+bool isAV1Codec(String codec) => codec.toLowerCase() == 'av1';
+
 class ScalabilityMode {
   late num spatial;