Fix matrix binary search missing values at row starts

[Miladkhoshdel]

Describe your change

• Add an algorithm?
• 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?

Fix mat_bin_search() missing a target that equals the first element of a row after the first row.

For example, mat_bin_search(3, [[1, 2], [3, 4]]) previously returned [-1, -1] instead of [1, 0].

The row-selection loop used <, stopping before searching a row whose first element equaled the target. Changing the condition to <= allows that row to be searched.

This PR changes one condition in one algorithm file. Existing doctests remain unchanged.

Validation:

• Existing doctests: 8 passed, 0 failed.
• 2,922 generated search cases passed.
• Row-start searches in an interleaved sorted matrix passed.
• Ruff lint and formatting checks for the changed file passed.
• git diff --check passed.

The repository-wide Ruff check still fails on the existing ICN001 error in maths/zellers_congruence.py, addressed separately by #15547.

Checklist

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• 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. — No new files added.
• 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 8 existing doctests pass locally.
• All new algorithms include at least one URL that points to Wikipedia or another similar explanation. — No new algorithms added.
• 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". — No linked issues to close.

[algorithms-keeper]

Multiple Pull Request Detected

@Miladkhoshdel, we are extremely excited that you want to submit multiple algorithms in this repository but we have a limit on how many pull request a user can keep open at a time. This is to make sure all maintainers and users focus on a limited number of pull requests at a time to maintain the quality of the code.

This pull request is being closed as the user already has an open pull request. Please focus on your previous pull request before opening another one. Thank you for your cooperation.

User opened pull requests (including this one): #15548, #15547, #15546, #15545