Fix matrix binary search at row starts

[sean0407]

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?

mat_bin_search(3, [[1, 2], [3, 4]]) currently returns [-1, -1] instead of [1, 0]. After the first row is searched, the loop condition matrix[index][0] < value stops when the target equals the first element of the next row, so that row is never searched. Using <= includes that boundary row.

A previous proposal for the same one-line correction, PR #15548, was closed by algorithms-keeper because that author already had multiple open PRs. It did not merge, and the upstream source still has the bug.

Verification

• Reproducible input and expected result: mat_bin_search(3, [[1, 2], [3, 4]]) -> [1, 0].
• The current source-level trace shows the < condition stops at row 1 before the binary search call; the updated <= condition reaches that call.
• GitHub compare confirms exactly one algorithm file changed, with 1 addition and 1 deletion.

Checklist

• I have read CONTRIBUTING.md.

• 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.)

• All filenames are in lowercase and use underscores. (No new files.)

• All function parameters and return values are annotated. (No signature changes.)

• All new algorithms include a reference URL. (No new algorithm.)

• If this pull request resolves an issue, include its closing keyword. (No linked issue.)