Update chaindb to use a slab allocator for small size buffers.

[greg7mdp]

Resolves #1049.

Now this integrates the changes from AntelopeIO/chainbase#54, which can be referred to for previous comments.

As the issue describes, the current chainbase does a lot of small buffer allocations directly through the bip allocator which hits the segment manager directly. Not only this is inefficient (the rbtree of free buffers need to be rebalanced for every alloc/free), it also has a higher memory overhead.

The slab allocators for small buffers (in the updated chainbase submodule) batch allocations of small buffers into larger blocks, reducing the fragmentattion within the shared memory segment, and providing better efficiency and a smaller memory footprint.

For comparison, here are some results comparing snapshot loading on my linux box (release build)

snapshot from Aug 11, 2024

	time (average)	chainbase memory usage	memory saving
main branch	55s	23.67GB	-
this branch	28s	22.41GB	5.3%

snapshot from Sept 29, 2024

	time (average)	chainbase memory usage	memory saving
main branch	392s	65.30GB	-
this branch	331s	63.12GB	3.3%

I also expect a slight performance increase for processing transactions, as the _undo_stack deque allocations used to go through the segment allocator as well (for blocks of 16 undo_state), and these allocations are now batched.

[ericpassmore]

Note:start
category: System Enhancements
component: Internal
summary: Improve chainbase to use utilize slab allocator for small buffers. Reduces memory contention and frequency of rebalancing.
Note:end