feat: implement session-level recording with self/bot audio filtering

- Add RecordingSession tracking for guild-level audio mixing
- Filter out self user and bot users before subscribing to audio streams
- Register segments with session metadata for post-processing
- Finalize recording sessions on connection destroy or explicit stop
- Update test mocks to properly simulate stream chain and constructors
- Remove mock-crc import (no longer needed with current dependencies)
- Add 'type: module' to package.json for ES module support

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

package.json

@@ -2,6 +2,7 @@
   "name": "discord-voice-recorder",
   "version": "1.0.0",
   "description": "Discord bot that joins a voice channel and records audio",
+  "type": "module",
   "main": "src/index.ts",
   "packageManager": "pnpm@10.25.0",
   "scripts": {