The allocation limits on MemoryAllocator were internal with no public
way to raise the 1 GB single-buffer default, and ApplyOptions was not
callable from external subclasses, which blocked custom allocators.
- Expose MemoryGroupAllocationLimitBytes, SingleBufferAllocationLimitBytes,
and AccumulativeAllocationLimitBytes with validated protected setters.
- Make ApplyOptions protected so derived allocators can accept options.
- Add MemoryAllocatorOptions.SingleBufferAllocationLimitMegabytes to raise
the contiguous buffer cap up to 2047 MB without a custom allocator.
- Add public-api tests that implement a complete external allocator.
- Add behavior tests for the new option and its validation.
James Jackson-South