Add TortoiseHareAlgo implementation with append, toString, and getMiddle methods (#6722)

* Create TortoiseHareAlgorithm.java

Implement TortoiseHareAlgo with append, getMiddle, and toString methods

- Added generic singly linked list with inner Node class
- Implemented append() to add elements
- Implemented getMiddle() using Tortoise-Hare approach
- Added toString() for readable list representation

* Create TortoiseHareAlgoTest.java

Add JUnit tests for TortoiseHareAlgo

- Verified append() and toString() output
- Tested getMiddle() for odd, even, and empty lists
- Ensured correct behavior and null handling

* Update README.md

Add TortoiseHareAlgo to linked list documentation

- Added TortoiseHareAlgo.java to file descriptions
- Described its purpose: finding middle element using Tortoise-Hare algorithm

* Rename TortoiseHareAlgorithm.java to TortoiseHareAlgo.java

Fixed build error

* Update TortoiseHareAlgoTest.java

Fixed line formatting build error

* Update TortoiseHareAlgoTest.java

Fixed line formatting build error

* Update TortoiseHareAlgo.java

Added {} after if statement instead of directly writing statement

* Update TortoiseHareAlgo.java

Fixed line formatting build error

* Update TortoiseHareAlgo.java

Added {} after if statement instead of directly writing statement

* Update TortoiseHareAlgoTest.java

Replace .* import with specific imports

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Co-authored-by: Deniz Altunkapan <deniz.altunkapan@outlook.com>