websocket: send/receive reducer & table ids instead of names

[Centril]

Description of Changes

Receive and send reducer ids and table ids as opposed to names in the SDK.

TODO:

• [x] Host implementation of the above.
• [x] Rust SDK implement of the above.
• [x] C# SDK implementation of the above, https://github.com/clockworklabs/com.clockworklabs.spacetimedbsdk/pull/178
• [ ] TS SDK implementation of the above

Fixes https://github.com/clockworklabs/SpacetimeDBPrivate/issues/1091.

API and ABI breaking changes

Yes.

[Centril]

Please update the PR description to match the template.

👍

• I would like to see a Rust SDK test added which verifies that it's possible to construct a connection and then immediately invoke a reducer, without first waiting for the on-connect callback. I would expect this to queue the reducer call until the handshake message is received. The code appears to do this correctly, but I want a test to make sure we don't regress it in the future.

This is exercised by the test exec_caller_always_notified which failed before I adjusted the SDK to first always process the handshake.