Minimize small allocations by dropping the tick Vecs from Resources

[james7132]

Objective

Column unconditionally requires three separate allocations: one for the data, and two for the tick Vecs. The tick Vecs aren't really needed for Resources, so we're allocating a bunch of one-element Vecs, and it costs two extra dereferences when fetching/inserting/removing resources.

Solution

Drop one level lower in ResourceData and directly store a BlobVec and two UnsafeCell<Tick>s. This should significantly shrink ResourceData (exchanging 6 usizes for 2 u32s), removes the need to dereference two separate ticks when inserting/removing/fetching resources, and can significantly decrease the number of small allocations the ECS makes by default.

This tentatively might have a non-insignificant impact on the CPU cost for rendering since we're constantly fetching resources in draw functions, depending on how aggressively inlined the functions are.

This requires reimplementing some of the unsafe functions that Column wraps, but it also allows us to delete a few Column APIs that were only used for Resources, so the total amount of unsafe we're maintaining shouldn't change significantly.

[alice-i-cecile]

This change makes sense to me, the unsafe is straightforward, and the docs are good. Curious to see if this measurably changes performance.

[JoJoJet]

Nice, this could be surprisingly impactful.

[james7132]

I'll run a full trace on these later to see if there's any tangible impact on rendering, but I ran a quick sanity check on the assembly output, and the removal of a bunch of allocation related machinery in resource insertion seems promising: james7132/bevy_asm_tests@main...11226-minimize-resource-allocations#diff-f4d513f091332848b18110a4e97729c2d725fef55a135820bc0a0e8cc56b88a7