Added branch_and_bound Algorithm

[iamdevdhanush]

Describe your change:

This pull request adds a Branch and Bound implementation for solving the 0/1 Knapsack problem in Python.

The algorithm uses a best-first search strategy with a priority queue and prunes non-promising branches using an upper bound calculated via a greedy (fractional knapsack) approach. The implementation is deterministic, well-documented, and includes a passing doctest.

• [x] Add an algorithm?
• [ ] Fix a bug or typo in an existing algorithm?
• [ ] Add or change doctests?
• [x] Documentation change?

Checklist:

• [x] I have read https://github.com/TheAlgorithms/Python/blob/master/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.
• [x] All new Python files are placed inside an existing directory.
• [x] All filenames are in all lowercase characters with no spaces or dashes.
• [x] All functions and variable names follow Python naming conventions.
• [x] All function parameters and return values are annotated with Python type hints.
• [x] All functions have doctests that pass the automated testing.
• [x] All new algorithms include at least one URL that points to Wikipedia or a similar explanation.
• [ ] This pull request resolves one or more open issues.

References

• https://en.wikipedia.org/wiki/Branch_and_bound
• https://en.wikipedia.org/wiki/Knapsack_problem