[WIP] Avro metadata #6502

Job	Run time
bench test	18m 39s
Rust build (all-features)	9m 34s
Check generated proto/fbs files are up to date	40s
Rust build (default features)	8m 10s
Rust build (with tokio dispatcher)	8m 19s
License Check and Audit Check	5m 5s
Rust build (with compio dispatcher)	8m 35s
miri	8m 45s
Rust build (with tokio+compio dispatcher)	8m 10s
Rust build (wasm32 with default features)	3m 24s
Python (lint)	3m 49s
Python (test)	6m 47s
Rust (docs)	2m 3s
Rust (lint)	37s
Rust (tests)	5m 55s
	1h 38m 32s

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