feat: switch to `tracing` #917

Job	Run time
Build docs	1m 18s
Clippy	56s
Rustfmt	15s
Test (MSRV)	5m 17s
Test (stable)	2m 4s
Test (beta)	1m 58s
Test (nightly)	1m 58s
Test (macOS)	2m 52s
Test (Windows)	4m 29s
Test (no features)	1m 15s
Test (all features - simdjson, cargo test --all-features --lib --tests --examples)	1m 24s
Test (native TLS, cargo test --all-features --features serenity/native_tls_backend --lib --tests ...	1m 29s
	25m 15s

Provide feedback