fix(binary_search): return first occurrence when duplicates exist

[MD-Mushfiqur123]

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• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
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When the binary_search function encounters a sorted list with duplicate values, it returns the first match found during the search (which depends on the midpoint calculation), rather than the first occurrence of the target value.

Fix

Instead of returning immediately when a match is found, continue searching to the left to find the first occurrence. The function now tracks the result with a result variable and continues narrowing the search window to the left after finding a match.

Testing

• All 62 existing doctests pass
• Added doctests for duplicate scenarios:
  • binary_search([1, 2, 2, 2, 3], 2) returns 1
  • binary_search([1, 1, 1, 2, 3], 1) returns 0

Fixes #13840