Added listener for flushing `Str` cache between requests

[tarampampam]

Description

Added

• Listener FlushStrCacheListener for flushing Str cache between requests

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I wrote unit tests for my code (if tests is required for my changes)
• [x] I have made changes in CHANGELOG.md file

[codecov[bot]]

Codecov Report

Merging #86 (3f05487) into master (c0b2715) will increase coverage by 0.36%. The diff coverage is 91.30%.

@@             Coverage Diff              @@
##             master      #86      +/-   ##
============================================
+ Coverage     77.72%   78.09%   +0.36%     
- Complexity      328      337       +9     
============================================
  Files            63       64       +1     
  Lines           826      849      +23     
============================================
+ Hits            642      663      +21     
- Misses          184      186       +2     

Impacted Files	Coverage Δ
src/Defaults.php	100.00% <ø> (ø)
src/Listeners/Traits/InvokerTrait.php	93.93% <88.88%> (-6.07%)	:arrow_down:
src/Listeners/FlushStrCacheListener.php	100.00% <100.00%> (ø)

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