feat: Add experimental rewrite of go2rtc live provider (MSE/WebRTC/MP4/MJPEG) (#2580)

- Closes #2556
- Closes #2450

**Key intended features:**
 - go2rtc compatible
- 100% test coverage to significantly improve ability to test, maintain
and work around browser weirdnesses (e.g. Safari).
 - Written from the ground up in the style of the rest of the project.

**To use:**
 - Change `live_provider` from `go2rtc` to `go2rtc-experimental`.

tests/components-lib/live/providers/go2rtc-experimental/utils/source-priority.test.ts

@@ -0,0 +1,76 @@
+import { describe, expect, it } from 'vitest';
+
+import type { StreamProfile } from '../../../../../../src/components-lib/live/providers/go2rtc-experimental/types';
+import { getPreferredSource } from '../../../../../../src/components-lib/live/providers/go2rtc-experimental/utils/source-priority';
+
+const createProfile = (overrides: Partial<StreamProfile>): StreamProfile => ({
+  hasVideo: false,
+  hasH265Video: false,
+  hasAudio: false,
+  hasAACAudio: false,
+  ...overrides,
+});
+
+describe('getPreferredSource', () => {
+  it('should prefer WebRTC when both offer equal H.264 video and audio', () => {
+    expect(
+      getPreferredSource(
+        createProfile({ hasVideo: true, hasAudio: true }),
+        createProfile({ hasVideo: true, hasAACAudio: true }),
+      ),
+    ).toBe('webrtc');
+  });
+
+  it('should prefer WebRTC H.265 over binary-source H.265', () => {
+    expect(
+      getPreferredSource(
+        createProfile({ hasVideo: true, hasH265Video: true }),
+        createProfile({ hasVideo: true, hasH265Video: true }),
+      ),
+    ).toBe('webrtc');
+  });
+
+  it('should prefer binary-source H.265 with audio over WebRTC H.264 with audio', () => {
+    expect(
+      getPreferredSource(
+        createProfile({ hasVideo: true, hasAudio: true }),
+        createProfile({ hasVideo: true, hasH265Video: true, hasAACAudio: true }),
+      ),
+    ).toBe('binary');
+  });
+
+  it('should prefer WebRTC when the binary source has no media', () => {
+    expect(
+      getPreferredSource(createProfile({ hasVideo: true }), createProfile({})),
+    ).toBe('webrtc');
+  });
+
+  it('should prefer the binary source when WebRTC has no video', () => {
+    expect(
+      getPreferredSource(
+        createProfile({ hasAudio: true }),
+        createProfile({ hasVideo: true }),
+      ),
+    ).toBe('binary');
+  });
+
+  it('should prefer the stream with audio when video is otherwise equal', () => {
+    expect(
+      getPreferredSource(
+        createProfile({ hasVideo: true }),
+        createProfile({ hasVideo: true, hasAACAudio: true }),
+      ),
+    ).toBe('binary');
+  });
+
+  it('should not count non-AAC MSE audio', () => {
+    // MSE opus audio (hasAudio true, hasAACAudio false) does not raise the
+    // binary-side score, so WebRTC video wins.
+    expect(
+      getPreferredSource(
+        createProfile({ hasVideo: true }),
+        createProfile({ hasVideo: true, hasAudio: true }),
+      ),
+    ).toBe('webrtc');
+  });
+});