Add Splay Tree implementation

- Self-adjusting binary search tree with splaying operations
- Implements all standard BST operations (insert, delete, search, min, max)
- Includes zig, zig-zig, and zig-zag rotation operations
- Amortized O(log n) time complexity for all operations
- Comprehensive doctests with 81 passing tests
- Performance demonstration showing locality of reference
- Includes tree visualization and traversal methods

Author: Prigoistic