feat: add race condition test with dynamic date selection (calcom#22533)

* feat: add race condition test with dynamic date selection

- Recreate race condition test from PR calcom#22401 for calendar-cache-serve booking flow
- Replace hardcoded TEST_DATE with dynamic first available slot selection
- Use getDynamicBookingDate function to select first available day dynamically
- Prevent test flakiness by avoiding hardcoded tomorrow dates
- Test validates concurrent booking prevention and cache functionality

Co-Authored-By: anik@cal.com <adhabal2002@gmail.com>

* fix: replace dynamic date selection with fixed future date for efficiency

Co-Authored-By: anik@cal.com <adhabal2002@gmail.com>

* Revert "fix: replace dynamic date selection with fixed future date for efficiency"

This reverts commit b4b7d35.

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Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: anikdhabal