Ensure that NAAJ works with spilling enabled and disabled.

I believe there are some gaps in test coverage here:

• Should be able to run a large NAAJ with spilling disabled (need to test both success and OOM cases)
• Test spilling cases:

• null_probe_rows_ does not fit in memory
• null_aware_probe_partition_ does not fit in memory along with other partitions
• null_aware_partition_ does not fit in memory along with other partitions

We should address these gaps before releasing the new buffer pool code to ensure we don't regress anything.