Fix config merger

[vjik]

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

Fix #153

[what-the-diff]

PR Summary

• Added new feature to handle duplication exceptions
  The change log has been updated to include a specific exception handling for situations involving 'Duplicate key' when using nested groups. This addition will effectively manage any duplication errors and improve overall functionality.

• Enhancement in Config.php
  Two new methods - shelve() and unshelve() have been added to Config.php. These methods, particularly useful for managing temporary storage spaces.

• Update in Merger.php
  A new storage property ($shelveStorage) has been added in the Merger.php file along with the same shelve() and unshelve() methods, further streamlining data management processes.

• New integrative tests and schemas
  To ensure that everything works perfectly, we've introduced a new test file (NestedGroupBug153Test.php) and setup files (di.php and di-web.php) in the tests/Integration/NestedGroupBug153 folder.

• Package management improvements
  A new composer.json file has been added in the tests/Integration/NestedGroupBug153/packages/a folder. With this, we now have better management and understanding of the project's dependencies.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (8ef9884) 100.00% compared to head (d457d2d) 100.00%.

Additional details and impacted files

@@             Coverage Diff             @@
##              master      #163   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity       277       277           
===========================================
  Files             22        22           
  Lines            728       725    -3     
===========================================
- Hits             728       725    -3     

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