Refactor red-black tree removal to reduce cyclomatic complexity

[AlexeyBasinger]

Describe your change:

Refactor the red–black tree deletion logic in data_structures/binary_tree/red_black_tree.py to reduce cyclomatic complexity and improve readability while preserving the existing behavior Main changes:

1. Extracted the deletion logic from remove into small helper methods: _remove_node, _remove_with_two_children, _remove_with_zero_or_one_child, _remove_red_leaf, _remove_black_leaf, _remove_black_node_with_red_child
2. Split _remove_repair into several case-specific helpers: _repair_red_sibling, _repair_black_parent_black_sibling_black_children, _repair_red_parent_black_sibling_black_children, _repair_inner_nephew, _repair_outer_nephew.
3. Added null-safety checks (for example, around sibling usage) to avoid potential None access.

• [ ] Add an algorithm?
• [x] Fix a bug or typo in an existing algorithm?
• [ ] Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• [ ] Documentation change?

Checklist:

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized.
• [x] I know that pull requests will not be merged if they fail the automated tests.
• [x] This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• [ ] All new Python files are placed inside an existing directory.
• [ ] All filenames are in all lowercase characters with no spaces or dashes.
• [ ] All functions and variable names follow Python naming conventions.
• [ ] All function parameters and return values are annotated with Python type hints.
• [ ] All functions have doctests that pass the automated testing.
• [ ] All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• [ ] If this pull request resolves one or more open issues then the description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".