logalloc: limit std segment allocations in debug mode
logalloc: limit std segment allocations in debug mode

Address Sanitizer has a global limit on the number of allocations
(note: not number of allocations less number of frees, but cumulative
number of allocations). Running some tests in debug mode on a machine
with sufficient memory can break that limit.

Work around that limit by restricting the amount of memory the
debug mode segment_pool can allocate. It's also nicer for running
the test on a workstation.

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