Exception raised by LatticeStripe.Testing.TestClock when a test-time
precondition fails — e.g., advance/2 is called with an unsupported
unit (:months, :years on Elixir 1.15), or no client is bound at the
call site.
Distinct from LatticeStripe.Error (which represents Stripe API
failures): TestClockError is purely a test-helper-level programming
error that surfaces inside the developer's ExUnit suite.