Improve ratelimiting in Synapse #1489

Job	Run time
changes	4s
changes	4s
check-lockfile	5s
check-lockfile	5s
lint-crlf	6s
lint-crlf	6s
lint-newsfile	32s
lint-newsfile	32s
Typechecking	1m 26s
Typechecking	1m 26s
check-schema-delta	42s
check-schema-delta	42s
check-sampleconfig	46s
check-sampleconfig	46s
lint	47s
lint	47s
lint-pydantic	46s
lint-pydantic	46s
lint-clippy	0s
lint-clippy	0s
lint-clippy-nightly	0s
lint-clippy-nightly	0s
lint-rustfmt	0s
lint-rustfmt	0s
linting-done	3s
linting-done	3s
calculate-test-jobs	8s
calculate-test-jobs	8s
trial-olddeps	7m 26s
trial-olddeps	7m 26s
portdb (3.8, 11)	3m 0s
portdb (3.8, 11)	3m 0s
portdb (3.11, 15)	2m 52s
portdb (3.11, 15)	2m 52s
cargo-bench	0s
cargo-bench	0s
cargo-test	0s
cargo-test	0s
complement (monolith, SQLite)	12m 45s
complement (monolith, SQLite)	12m 45s
complement (monolith, Postgres)	13m 15s
complement (monolith, Postgres)	13m 15s
trial-pypy	0s
trial-pypy	0s
complement (workers, Postgres)	20m 8s
complement (workers, Postgres)	20m 8s
trial (3.8, sqlite, all)	4m 44s
trial (3.8, sqlite, all)	4m 44s
sytest (focal)	8m 27s
sytest (focal)	8m 27s
trial (3.8, postgres, 11, all)	10m 50s
trial (3.8, postgres, 11, all)	10m 50s
trial (3.8, sqlite)	4m 8s
trial (3.8, sqlite)	4m 8s
sytest (focal, postgres)	10m 28s
sytest (focal, postgres)	10m 28s
sytest (focal, multi-postgres, workers)	13m 52s
sytest (focal, multi-postgres, workers)	13m 52s
sytest (focal, multi-postgres, workers, asyncio)	6h 0m 4s
sytest (focal, multi-postgres, workers, asyncio)	19m 9s
export-data	2m 17s
export-data	2m 17s
tests-done	2s
tests-done	4s
	10h 18m 33s

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