hll memory estimate in MB instead of Bytes

[jshencode]

this drastically under estimate memory usage for hll query and cause out of memory situation during massive hll query hits, such as weekly hll contracts

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 71.89%. Comparing base (56108d0) to head (6b14771). Report is 47 commits behind head on master.

Files with missing lines	Patch %	Lines
query/aql_processor.go	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #312 +/- ## ======================================== Coverage 71.88% 71.89% ======================================== Files 166 166 Lines 23252 23367 +115 ======================================== + Hits 16714 16799 +85 - Misses 5246 5275 +29 - Partials 1292 1293 +1 ```

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