Add the ability of using prefixes in pubsub channel names

[karolyi]

Hey,

the idea here is that I'm using FreeBSD where I have one Valkey instance that software uses. This module wasn't able to use prefixes for channels, which can lead to collisions, given I'd have more livekit deployments.

I'm already making changes to livekit itself to feature the prefix option, please merge this and update its dependency when able.

Next up I'll make a PR for livekit itself.

[CLAassistant]

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[karolyi]

The tests fail but not caused by this PR:

CI flake: TestRPC/Redis/RPC — not caused by this PR

The failing assertion (counter expected 3, got 2) is a pre-existing timing race in the Redis bus, not a regression from the channel-prefix change here.

Root cause: redisMessageBus.subscribe() (internal/bus/bus_redis.go) is fire-and-forget — it marks the channel dirty and returns immediately, while the actual Redis SUBSCRIBE is issued later by the async writeWorker/reconciler. server.RegisterHandler returning gives no guarantee the SUBSCRIBE has actually landed on the Redis connection yet.

internal/test/psrpc_test.go's testRPC papers over this with a fixed time.Sleep between registering handlers and firing the request, guessing how long propagation takes. This commit already widened that sleep from 1s to 2s (see commit message) to reduce exactly this flake — but 2s still isn't enough headroom on some CI runners, so it can still fire before all 3 servers' subscriptions are live, and one server silently misses the fan-out request.

Not a logic bug in the new code: the multi-RPC path involved here (multi=true, requireClaim=false) doesn't touch the claim/skip-claim logic at all — that's confirmed since RequireClaim is false for multiRpc in the test.

Options considered, none applied yet:

• Bump the sleep further (cheap, still nondeterministic)
• Make subscribe block until the reconciler confirms the SUBSCRIBE landed (real fix, touches bus_redis.go internals)

Flagging for visibility — happy to implement either fix if wanted.