Prefer Map dictionaries

[RobinTail]

For performance reasons and modernity.

[coveralls-official]

coverage: 100.0%. remained the same
when pulling d86dd0e on prefer-map-dict
into d118e3b on master.

[RobinTail]

That gave 3% performance improvement to ensureUniqOperationId for "create" + "update" case.

   ✓ Experiment (2) 11627ms
     name              hz     min     max    mean     p75     p99    p995    p999     rme  samples
   · original  164,226.13  0.0057  0.3901  0.0061  0.0061  0.0069  0.0076  0.0122  ±0.12%   821131
   · featured  168,904.64  0.0055  0.4062  0.0059  0.0059  0.0070  0.0086  0.0123  ±0.14%   844524   fastest

When testing on thousands of calls, the expected benefit is above 13%

   ✓ Experiment (2) 1480ms
     name              hz     min     max    mean     p75     p99    p995    p999     rme  samples
   · original  330,083.87  0.0024  2.9041  0.0030  0.0029  0.0037  0.0046  0.0187  ±2.46%   165042
   · featured  373,361.59  0.0023  1.3683  0.0027  0.0026  0.0029  0.0031  0.0158  ±2.05%   186681   fastest

[RobinTail]

ok

[RobinTail]

ready