[PATCH] Add memory usage reporting to VACUUM VERBOSE

Hi,

I would like to propose a patch that adds memory usage reporting to
VACUUM VERBOSE output. This helps users understand how much memory
is being used for dead tuple tracking and whether memory limits are
being hit during vacuum operations.

I have tested this patch with both serial and parallel VACUUM:
- Serial VACUUM with two maintenance_work_mem settings
- Parallel VACUUM with two maintenance_work_mem settings
- Cases with and without memory resets

Test cases are included showing:
1. Reset behavior with constrained memory (64KB)
2. No reset behavior with ample memory (64MB)
3. Both serial and parallel VACUUM scenarios

I look forward to your feedback.

Best regards,
Tatsuya Kawata