Add more specific psalm type for QueryFunctionsInterface::count() result

[vjik]

Q	A
Is bugfix?	❌
New feature?	❌
Breaks BC?	❌

[what-the-diff]

PR Summary

• Enhanced function definition in QueryFunctionsInterface class
  The 'count()' function in the QueryFunctionsInterface class now has a more specific type associated with it. This promotes increased accuracy during code execution.

• Added a code annotation in Query class
  An annotation - '@psalm-var non-negative-int|string' - has been added in the 'count()' function located in the Query class. Annotations help developers better understand the intended function use and output expectation. In this case, it indicates that the function should return a non-negative integer or a string.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (4a08ca3) 99.64% compared to head (134d399) 99.55%.
Report is 2 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #810      +/-   ##
============================================
- Coverage     99.64%   99.55%   -0.10%     
- Complexity     1270     1277       +7     
============================================
  Files            63       63              
  Lines          3106     3120      +14     
============================================
+ Hits           3095     3106      +11     
- Misses           11       14       +3     

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