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

[vjik]

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

[what-the-diff[bot]]

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[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

```diff @@ 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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