feat: add basic chunked audio send in /playback endpoint

- add `Library::get_track_by_id()`
- add futures as a dependency

Cargo.toml

@@ -7,6 +7,7 @@ edition = "2024"
 diesel = { version = "2.3.14", features = ["sqlite", "returning_clauses_for_sqlite_3_35"] }
 diesel_migrations = { version = "2.3.2", features = ["sqlite"] }
 dotenvy = "0.15.7"
+futures = "0.3.34"
 lofty = "0.25.4"
 ntex = { version = "4.4.0", features = ["tokio"] }
 serde = { version = "1.0.229", features = ["derive"] }