Ruby

Remove extra sentinel from shape capacities

This isn't a 0 terminated list anymore because we iterate over
heaps_count directly. So we don't need to allocate an extra byte for the
sentinel

Make it obvious that field count guard is for debug

This is because when RVALUE_OVERHEAD is positive, ie. when
RACTOR_CHECK_MODE is enabled and we need to store the pointer to the
owning ractor, we need to make sure there is enough space to store it....

Replace sweeping_heaps map with a counter

We implemented some bit twiddling logic with an unsigned int to have a
neat way of tracking which heaps were currently sweeping, but we
actually don't need to care which heap is sweeping right now, just
whether some are or not, so we can replace this with a counter.

Use the pre-processor to generate slot sizes and reciprocals

Fix zjit hir tests

Allow flex in heap growth threshold

Add a 7/8 multiplier to the min_free_slots checks in
gc_sweep_finish_heap and gc_marks_finish, allowing heaps to be up to
~12.5% below the free slots target without triggering a major GC or
forced growth.

With 12 heaps instead of 5, each heap independently hitting the exact...

Cache has_sweeping_pages as a bitfield

Update tests for new pool layout

Introduce RVALUE_SIZE GC constant

Add GC::INTERNAL_CONSTANTS[:RVALUE_SIZE] to store the usable size
(excluding debug overhead) of the smallest pool that can hold a standard
RVALUE.

Introduce power-of-two size pools

Replace the RVALUE_SLOT_SIZE-multiplier based pool sizes with explicit
power-of-two (and near-power-of-two) slot sizes. On 64-bit this gives
12 heaps (32, 40, 64, 80, 96, 128, 160, 256, 512, 640, 768, 1024)
instead of 5, providing finer granularity and less internal...