tor/changes/laplace-edge-cases

  o Minor bugfixes:
    - Handle edge cases in the laplace functions:
       * avoid division by zero
       * avoid taking the log of zero
       * silence clang type conversion warnings using round and trunc
       * consistently check for overflow in round_*_to_next_multiple_of
    - Add tests for laplace edge cases:
       * check add_laplace_noise with maximal values
       * check round_*_to_next_multiple_of with additional values
       * check round_*_to_next_multiple_of with maximal values
      Related to HS stats in #13192.