Add ArrayHelper::restrictedMerge()

[vjik]

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

[what-the-diff]

PR Summary

• Added a new method for merging arrays
  A new method named restrictedMerge() has been introduced that can merge multiple arrays together, layer by layer, till a specified depth. This method combines elements with matching string keys and appends elements with number keys. We've also made sure to test this new functionality through various unit tests.

• Enhanced the existing method for merging arrays
  The previous merge() method has now been upgraded to use a new auxiliary method named doMerge(). This makes the code more streamlined and easier to maintain.

• Introduced a supporting helper method
  A new helper method doMerge() has been added, tasked with handling the complex logic of merging operations. This method is leveraged by both merge() and restrictedMerge() methods to execute their tasks.

• Included multiple unit tests
  Added an extensive set of unit tests for the restrictedMerge() method. These tests put the method under different conditions to ensure it works consistently and reliably.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3e9640a) 99.75% compared to head (b0c65e3) 99.76%.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #139   +/-   ##
=========================================
  Coverage     99.75%   99.76%           
- Complexity      208      212    +4     
=========================================
  Files             4        4           
  Lines           415      422    +7     
=========================================
+ Hits            414      421    +7     
  Misses            1        1           

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