fix: replace binarySearchByDateEqualOrNearestGreater with findIndexInSortedArray \w midpoint match

[arnautov-anton]

This PR removes and replaces binarySearchByDateEqualOrNearestGreater with universal findIndexInSortedArray function and enables exact matching by checking midpoint.

Changes to channel and channel_state tests are to ensure proper order of generated messages (added created_at to each generated message with proper offset).