wip: add uncached queries

[cBournhonesque]

Objective

• Adds uncached queries
• These queries can be contrasted with the current cached Queries: every time a query operation is done on cached queries, they start by iterating through new archetypes to check which of these new archetypes match the query.
  • when we do an operation on a cached query (iter/get/etc.), we use the cached metadata of sorted archetypes
  • for uncached query, we instead go through world archetypes from scratch to check which archetypes match the query. Note that we do not go through all the archetypes because we can use the ComponentIndex to reduce the number of archetypes that we have to go through.

Solution

• Implements uncached queries by adding a 3rd generic QueryCache to QueryState. That generic can essentially have 2 values: CacheState or Uncached.

I opted for this so that:

• we statically know if the query is cached or uncached so we don't pay the cost of if is_cached() calls
• we don't need to write new implementations for all the QueryState functions, only a couple of functions change and are implemented differently for QueryState<CacheState> vs QueryState<Uncached>

NOTE:

• the PR is still WIP (I'm getting some lifetime issues when trying to create the QueryIterationCursor object + it needs some polishings, tests, benchmarks)

[james-j-obrien]

Ignoring the WIP nature of the PR, this seems like broadly the correct approach to me i.e. splitting up the query state such that the "cache" portion is responsible for managing a list of storages to iterate.

Having an additional generic on all these query related structs and traits is an ergonomic hit, the bigger these definitions get the "scarier" they get in the sense that they become harder and harder to grok, but none of the alternatives are free either.

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[alice-i-cecile]

As SME-ECS, I'm broadly on board with this direction and excite to see this evolve!

[cBournhonesque]

Updated the PR to make the tests pass.

Things i'd like to change:

• ideally not add a 3rd generic to QueryState
• we realistically only have 2 implementations for QueryCache, so maybe we don't need a trait
• split_cache is very unsafe and miri errors on it
• maybe we can just have a UncachedQuery and a CachedQuery that contains it + the cache?

[alice-i-cecile]

maybe we can just have a UncachedQuery and a CachedQuery that contains it + the cache?

This seems like a simpler design. Explore that and report back?