perf(zero-cache): negotiate cumulative stream acks

[Karavil]

what changed

Adds negotiated cumulative ACKs for the stream transport. New clients request cumulative ACKs, but only enable them after the server sends the capability frame. Old v6 servers therefore keep receiving per-message ACKs.

benchmark output

medium-wide-batch-pressure, 15s, compared to v6 websocket batch frames:

tx/s: 2,099.4 -> 2,781.5
rows/s: 41,987.6 -> 55,629.2
fanout msg/s: 68,585.4 -> 88,968.3
websocket ACKs: 1,046,498 -> 731
process CPU utilization: 1.780 -> 1.583
reconnect catchup to join: 275.1 ms -> 216.7 ms

validation

pnpm exec vitest --project='*no-pg*' run src/types/streams.test.ts bench/rm-vs-load/config.test.ts bench/rm-vs-load/scenarios.test.ts bench/rm-vs-load/workloads.test.ts
pnpm exec vitest --project='*15*' run src/services/change-streamer/change-streamer-http.pg.test.ts
pnpm run check-types

[Karavil]

Replaced by rocicorp/mono PRs rocicorp#6070 through rocicorp#6078.