Reimplement: websocket: send/receive reducer & table ids instead of names (take 2)

This issue tracks reimplementation of the work from stale PR #1940, which is being closed because it is too out of date to merge directly.

    Original PR: https://github.com/clockworklabs/SpacetimeDB/pull/1940
    Original author: @Centril
    Original branch: `centril/name-keyed-websocket-use-ids`
    Base branch: `master`

    ## Original PR summary

    # Description of Changes

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

Alternative to https://github.com/clockworklabs/SpacetimeDB/pull/1883 which is more efficient, but also uses indices internally rather than strings, making the diff larger.

API and ABI breaking changes

Yes.

    ## Follow-up

    - Reimplement this change in a fresh PR against current `master`.
    - Carry forward any still-relevant context from the original PR discussion and review.
    - Link the new implementation PR back to the original stale PR for historical context.

Start by reviewing stale PR #1940, its discussion, and the centril/name-keyed-websocket-use-ids branch, then compare the proposal with current master. Reimplement the still-relevant change in a fresh PR, account for the documented API and ABI break, and link the new implementation back to PR #1940.