feat: Faster JSON dumps in `format_message` with `msgspec` #5981

Job	Run time
External Tests	0s
Test on 3.8 (tests) / ubuntu-latest / SQLAlchemy: 2	39s
Test on 3.9 (tests) / ubuntu-latest / SQLAlchemy: 2	40s
Test on 3.10 (tests) / ubuntu-latest / SQLAlchemy: 2	47s
Test on 3.11 (tests) / ubuntu-latest / SQLAlchemy: 2	58s
Test on 3.12 (tests) / ubuntu-latest / SQLAlchemy: 2	38s
Test on 3.8 (tests) / macos-latest / SQLAlchemy: 2	1m 10s
Test on 3.9 (tests) / macos-latest / SQLAlchemy: 2	53s
Test on 3.10 (tests) / macos-latest / SQLAlchemy: 2	40s
Test on 3.11 (tests) / macos-latest / SQLAlchemy: 2	39s
Test on 3.12 (tests) / macos-latest / SQLAlchemy: 2	38s
Test on 3.8 (tests) / windows-latest / SQLAlchemy: 2	1m 53s
Test on 3.9 (tests) / windows-latest / SQLAlchemy: 2	1m 37s
Test on 3.10 (tests) / windows-latest / SQLAlchemy: 2	2m 10s
Test on 3.11 (tests) / windows-latest / SQLAlchemy: 2	2m 6s
Test on 3.12 (tests) / windows-latest / SQLAlchemy: 2	2m 10s
Test on 3.12 (tests) / ubuntu-latest / SQLAlchemy: 1	36s
Test on 3.12 (doctest) / ubuntu-latest / SQLAlchemy: 2	37s
Test on 3.12 (mypy) / ubuntu-latest / SQLAlchemy: 2	44s
Test on 3.12 (deps) / ubuntu-latest / SQLAlchemy: 2	21s
Coverage	23s
	20m 19s

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