Improve FHIR Search Count Performance

[alexanderkiel]

FHIR Search queries using _summary=count with a single search parameter are already fast. On a properly spaced system about 2 million resources can be counted per second.

However, if the FHIR search query contains more than one search parameter, the performance was about 10 times slower.

With this PR, the performance will be on the same level as for queries with a single search parameter. This is achieved by parallelise also such queries.

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (c06ca74) 95.85% compared to head (9b05ebe) 95.85%.
Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1466      +/-   ##
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- Coverage    95.85%   95.85%   -0.01%     
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  Files          245      245              
  Lines        15836    15834       -2     
  Branches       335      335              
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- Hits         15180    15177       -3     
- Misses         321      322       +1     
  Partials       335      335              

Files	Coverage Δ
modules/db/src/blaze/db/impl/search_param.clj	100.00% <100.00%> (ø)
...ules/db/src/blaze/db/impl/search_param/chained.clj	100.00% <100.00%> (ø)
.../db/impl/search_param/composite/token_quantity.clj	97.05% <100.00%> (ø)
...aze/db/impl/search_param/composite/token_token.clj	100.00% <100.00%> (ø)
modules/db/src/blaze/db/impl/search_param/date.clj	98.38% <100.00%> (ø)
modules/db/src/blaze/db/impl/search_param/has.clj	100.00% <100.00%> (ø)
modules/db/src/blaze/db/impl/search_param/list.clj	100.00% <100.00%> (ø)
...dules/db/src/blaze/db/impl/search_param/number.clj	100.00% <100.00%> (ø)
...les/db/src/blaze/db/impl/search_param/quantity.clj	96.42% <100.00%> (ø)
...dules/db/src/blaze/db/impl/search_param/string.clj	96.49% <100.00%> (ø)
... and 4 more

... and 1 file with indirect coverage changes