perf: optimize date range intersection algorithm from O(n²) to O(n log n) (calcom#22076)

* feat: optimize date range intersection algorithm from O(n²) to O(n log n)

- Replace nested forEach loops with two-pointer approach
- Sort arrays once and traverse efficiently
- Maintains exact same functionality and API
- Improves performance for team scheduling scenarios

Co-Authored-By: keith@cal.com <keithwillcode@gmail.com>

* feat: add comprehensive stress test for intersect function performance

- Add performance comparison test showing 22x improvement from O(n²) to O(n log n)
- Include edge cases testing for correctness validation
- Test with realistic data sizes (50 date ranges per user)
- Demonstrate identical results between old and new algorithms
- Provide timing measurements and performance logging

Co-Authored-By: keith@cal.com <keithwillcode@gmail.com>

* refactor: update stress test to focus on optimized algorithm performance

- Remove old O(n²) algorithm comparison logic from test
- Focus stress test on current optimized intersect function performance
- Test with 400 total date ranges (4 users × 100 ranges each)
- Maintain realistic data sizes for team scheduling scenarios
- Execution time: 10.33ms for 400 ranges with 97 intersections found

Co-Authored-By: keith@cal.com <keithwillcode@gmail.com>

* docs: restore explanatory comment in intersect function

- Add back comment explaining intersection logic as requested in PR review
- Comment clarifies when intersected time ranges are added to results array
- Addresses GitHub feedback from hbjORbj to revert comment removal

Co-Authored-By: keith@cal.com <keithwillcode@gmail.com>

* refactor: remove unnecessary intersectNew variable in edge cases test

- Use intersect function directly instead of intersectNew variable assignment
- Addresses GitHub feedback from keithwillcode to clean up test code
- No functional changes to test logic or assertions

Co-Authored-By: keith@cal.com <keithwillcode@gmail.com>

* test: add comprehensive test coverage for intersect function

- Add 27 comprehensive test cases covering all edge cases and scenarios
- Test empty inputs, single arrays, overlapping ranges, containment
- Add team scheduling scenarios and performance testing
- Test unsorted input handling, cross-day scenarios, time precision
- Ensure comprehensive coverage without knowing algorithm implementation
- All tests pass with optimized O(n log n) algorithm
- Performance test shows 8.50ms execution time for 400 date ranges

Co-Authored-By: keith@cal.com <keithwillcode@gmail.com>

* perf: improve intersect function in slots (calcom#22087)

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Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: Udit Takkar <53316345+Udit-takkar@users.noreply.github.com>
Co-authored-by: Benny Joo <sldisek783@gmail.com>

Author: 4 people