MOD-9169 Do not double count used capacity of containers in memory stats

[ephraimfeldblum]

MOD-9169
re redis/docs#1305

Some memory of JSON values is double counted when stored in containers (arrays or objects). They are accounted for once in the capacity of the container, and then again when recursively counting the used memory of the values stored within the container.

Fix:
Separate the top-level call from recursive calls to get_memory(). The top-level object must account for its own size_of::<IValue>(). Any recursive call made have already accounted for that memory, so they do not need to add it in.

[codecov]

Codecov Report

Attention: Patch coverage is 88.46154% with 3 lines in your changes missing coverage. Please review.

Project coverage is 78.11%. Comparing base (c94ee01) to head (8abcb50).
Report is 24 commits behind head on master.

Files with missing lines	Patch %	Lines
redis_json/src/ivalue_manager.rs	88.46%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1329      +/-   ##
==========================================
- Coverage   78.37%   78.11%   -0.26%     
==========================================
  Files          15       15              
  Lines        4004     3871     -133     
==========================================
- Hits         3138     3024     -114     
+ Misses        866      847      -19     

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