perf(JoinInner): use AVs for keys instead of PVs

[Centril]

Description of Changes

1. Reuse join_inner logic from spacetimedb_vm.
2. Dedup query tests slightly.
3. Precompute ColIds in join_inner and don't recompute it for every element.
4. Store AlgebraicValue keys in JoinInner as opposed to ProductValue. This removes an allocation per map entry.
5. Make JoinInner callbacks infallible.
6. In JoinInner::next, avoid clones unless necessary.

3-6 collectively, but primarily 4, results in the following perf improvements compared to HEAD~1 on i7-7700K, 64GB RAM:

incr-join               time:   [788.24 ns 790.71 ns 794.34 ns]
                        change: [-15.369% -14.407% -13.168%] (p = 0.00 < 0.05)
                        Performance has improved.

API and ABI breaking changes

None

Expected complexity level and risk

1

[kazimuth]

LGTM 👍

[kazimuth]

This can't return &AlgebraicValue because it might be freshly allocated, right?

[Centril]

Indeed, it could at most return Cow<'_, AV> and we might want to attempt that in a follow up and see if it is beneficial.