Add simple thread-safe queue implementation

[prashantpiyush1111]

This PR adds a simple thread-safe queue implementation using Java synchronization.

Features:

• Node-based linked list implementation
• Thread-safe enqueue and dequeue using synchronized methods
• Basic operations: enqueue, dequeue, and isEmpty
• Simple and educational design

Motivation:

This implementation helps demonstrate:

• Mutual exclusion using synchronized
• Avoidance of race conditions
• Behavior of data structures in a multithreaded environment

A simple test example is also included to show multithreaded usage.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.58%. Comparing base (b3e31b5) to head (3293397).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7390      +/-   ##
============================================
+ Coverage     79.53%   79.58%   +0.04%     
- Complexity     7176     7195      +19     
============================================
  Files           798      800       +2     
  Lines         23467    23504      +37     
  Branches       4617     4619       +2     
============================================
+ Hits          18665    18706      +41     
+ Misses         4055     4054       -1     
+ Partials        747      744       -3     

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