Sliding sync: Add classes for per-connection state #2737

Job	Run time
changes	2s
check-lockfile	7s
lint-crlf	7s
lint-newsfile	34s
check-schema-delta	37s
Typechecking	1m 32s
lint	6m 22s
lint-pydantic	50s
check-sampleconfig	45s
lint-clippy	0s
lint-clippy-nightly	0s
lint-readme	0s
lint-rustfmt	0s
linting-done	2s
calculate-test-jobs	6s
trial-olddeps	8m 3s
portdb (3.8, 11)	2m 52s
complement (monolith, SQLite)	12m 50s
complement (monolith, Postgres)	14m 24s
complement (workers, Postgres)	20m 9s
portdb (3.11, 15)	2m 50s
cargo-bench	0s
cargo-test	0s
trial-pypy	0s
trial (3.8, sqlite, all)	4m 59s
sytest (focal)	8m 46s
trial (3.8, postgres, 11, all)	12m 0s
sytest (focal, postgres)	10m 19s
trial (3.8, sqlite)	4m 58s
sytest (focal, multi-postgres, workers)	14m 0s
sytest (focal, multi-postgres, workers, asyncio)	19m 7s
export-data	2m 2s
tests-done	3s
	2h 28m 26s

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