Improve query performance and add caching support

[Universal-Omega]

• Add ability to set maximum query time
• Add support for query cache
• Add pool counter support to limit query concurrency — usage of this would require additional setup

Additional changes:

• Fix all MediaWiki.ControlStructures.AssignmentInControlStructures.AssignmentInControlStructures PHPCS violations, and enable it
  • Because some of the conversion of while to foreach is required for the caching support change
• Unmark composer-test as experimental in CI
• Rename Query::$DB property to Query::$dbr
• Remove unused Parse::$DB property
• Update README.md
  • Add documentation for new configuration
  • Minor markdown and wording changes
• Some additional minor cleanup

[codecov-commenter]

Codecov Report

Merging #107 (c89816c) into master (cd764c2) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff            @@
##             master    #107   +/-   ##
========================================
  Coverage      0.00%   0.00%           
- Complexity     1559    1563    +4     
========================================
  Files            23      23           
  Lines          4323    4355   +32     
========================================
- Misses         4323    4355   +32     

Impacted Files	Coverage Δ
includes/Article.php	0.00% <0.00%> (ø)
includes/DynamicPageListHooks.php	0.00% <ø> (ø)
includes/LST.php	0.00% <0.00%> (ø)
includes/Logger.php	0.00% <0.00%> (ø)
includes/Parse.php	0.00% <0.00%> (ø)
includes/Query.php	0.00% <0.00%> (ø)

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