Small fix to decrease memory allocation

[systay]

Description

Minimal change in how we gather which tables have been used by a query.

                                  │  ../before  │              ../after              │
                                  │   sec/op    │   sec/op     vs base               │
Planner/from_cases.json-gen4-20     7.490m ± 1%   7.436m ± 1%       ~ (p=0.089 n=10)
Planner/filter_cases.json-gen4-20   149.7m ± 1%   150.0m ± 1%       ~ (p=0.912 n=10)
Planner/large_cases.json-gen4-20    468.0µ ± 0%   469.9µ ± 1%       ~ (p=0.218 n=10)
Planner/aggr_cases.json-gen4-20     13.26m ± 1%   13.21m ± 1%       ~ (p=0.105 n=10)
Planner/select_cases.json-gen4-20   10.54m ± 1%   10.48m ± 1%       ~ (p=0.089 n=10)
Planner/union_cases.json-gen4-20    3.875m ± 0%   3.824m ± 1%  -1.32% (p=0.000 n=10)
geomean                             8.108m        8.077m       -0.39%

                                  │  ../before   │              ../after               │
                                  │     B/op     │     B/op      vs base               │
Planner/from_cases.json-gen4-20     4.546Mi ± 0%   4.541Mi ± 0%  -0.11% (p=0.000 n=10)
Planner/filter_cases.json-gen4-20   19.74Mi ± 0%   19.73Mi ± 0%  -0.06% (p=0.000 n=10)
Planner/large_cases.json-gen4-20    274.1Ki ± 0%   274.4Ki ± 0%  +0.12% (p=0.000 n=10)
Planner/aggr_cases.json-gen4-20     7.245Mi ± 0%   7.241Mi ± 0%  -0.06% (p=0.000 n=10)
Planner/select_cases.json-gen4-20   6.152Mi ± 0%   6.138Mi ± 0%  -0.22% (p=0.000 n=10)
Planner/union_cases.json-gen4-20    2.236Mi ± 0%   2.231Mi ± 0%  -0.19% (p=0.000 n=10)
geomean                             3.657Mi        3.654Mi       -0.09%

                                  │  ../before  │              ../after              │
                                  │  allocs/op  │  allocs/op   vs base               │
Planner/from_cases.json-gen4-20     107.4k ± 0%   107.0k ± 0%  -0.34% (p=0.000 n=10)
Planner/filter_cases.json-gen4-20   523.4k ± 0%   522.7k ± 0%  -0.15% (p=0.000 n=10)
Planner/large_cases.json-gen4-20    10.55k ± 0%   10.49k ± 0%  -0.56% (p=0.000 n=10)
Planner/aggr_cases.json-gen4-20     165.7k ± 0%   165.4k ± 0%  -0.18% (p=0.000 n=10)
Planner/select_cases.json-gen4-20   143.2k ± 0%   142.3k ± 0%  -0.63% (p=0.000 n=10)
Planner/union_cases.json-gen4-20    52.40k ± 0%   52.05k ± 0%  -0.66% (p=0.000 n=10)
geomean                             95.05k        94.65k       -0.42%

Related Issue(s)

#16789

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
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• Tests were added or are not required
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• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.93%. Comparing base (6fc808d) to head (39c91e6).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16791      +/-   ##
==========================================
+ Coverage   68.91%   68.93%   +0.01%     
==========================================
  Files        1566     1566              
  Lines      201855   201886      +31     
==========================================
+ Hits       139113   139163      +50     
+ Misses      62742    62723      -19     

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