feat: Add Splay Tree implementation

[JKjk555]

This PR adds a complete implementation of Splay Tree, including:

• Core splay operations (zig, zig-zig, zig-zag rotations)
• Standard BST operations: insert, delete, search, find min/max
• In-order traversal, size/height calculation, tree visualization
• Test cases demonstrating all functionalities

Closes #13760

[algorithms-keeper]

Closing this pull request as invalid

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