Improve compatibility with PHP 8.4

[roxblnfk]

🔍 What was changed

• Fix deprecated nullable types

Related issue: #213

[codecov]

Codecov Report

Attention: Patch coverage is 93.54839% with 2 lines in your changes missing coverage. Please review.

Project coverage is 95.42%. Comparing base (bdb9d34) to head (3822f76).
Report is 4 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
src/Driver/ReadonlyHandler.php	0.00%	1 Missing ⚠️
src/Query/Traits/JoinTrait.php	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##                2.x     #214   +/-   ##
=========================================
  Coverage     95.42%   95.42%           
  Complexity     1866     1866           
=========================================
  Files           130      130           
  Lines          5204     5204           
=========================================
  Hits           4966     4966           
  Misses          238      238           

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