feat/river schema v2 compatibility

[blast-hardcheese]

Why

River Schema v2 compatibility so we can start getting rid of the compatibility layer.

What changed

Client

Significantly restructured the river.v2.*.

• Nearly all asyncio.Lock's have been removed
• Background tasks are now cleaned up correctly, which should reduce the amount of noise around tasks being GC'd while they're still running
• Move websocket state ownership from Client transport down into Client Session. This significantly simplifies transparent reconnects, since we don't need to coordinate state shifting.
• There are four background tasks:
  • Heartbeat checker. This keeps track of whether we've gotten any heartbeats from the server recently.
  • "Close session" checker. This keeps track of whether we've exceeded the grace period for transparent reconnects.
  • Buffered message sender. One downside with the previous implementation was that we had a race on sending messages over the websocket, since we had no coordination between calls to send_message when called concurrently, so we'd end up with seq bound and incremented but then messages would become out-of-order by the time the ws.send method returned. Now we just atomically append to a deque as we push onto the send buffer, and when we get a confirmation from the ws library we move the message over to an ack buffer (also a deque) waiting for incoming messages from the server to allow us to drain.

Codegen

• init is now required for all method types, input is now optional. This simplifies rpc and stream codegen.
• Fixed some bugs where init was being used in input position and vice versa.
• Swapping f"'{foo}'" encoding for f"{repr(foo)}", giving greater safety post-generation (to avoid situations where f"'{None}'" gets rendered as "None". f"{repr(None)}" would render as None which would fail typechecks.)

Test plan

Manually ran codegen against v2 generated schemas, everything typechecks.

[masad-frost]

Do you wanna set up a different base branch in case we need to send a patch against main?

[blast-hardcheese]

Do you wanna set up a different base branch in case we need to send a patch against main?

If we need to patch, we should do feature patches off previous release tags. Since we're reserving 1.x for GA, I can follow the 0.200.0 strategy in this repo for schema-v2 releases.

Doing that though would suggest that we do at least a halfway decent pass at the v2 server codegen as well though. Given what we discussed supporting v1/v2 using a naive shim doesn't seem too bad, probably can get that done this week.

Wdyt?

[blast-hardcheese]

Five remaining flakes in babel:

flaked:
- StreamDisconnectNotifs
- RpcDisconnectNotifs
- ShouldNotSendBufferAfterSessionDisconnect
- ComplexSituation
- UploadDisconnectNotifs