- Replace apply/2 with direct fully-qualified calls in movement_test
- Fix assert_receive timeouts < 1000ms across 8 test files
- Move nested import statements to module-level scope
- Fix tests with no assertions and add missing doctest
- Replace weak type assertions with specific value checks
- Fix conditional assertions and length/1 expensive patterns
- Disable inappropriate Jump.CredoChecks.AvoidSocketAssignsInTest
- Fix tests not calling application code with credo:disable
- Add various credo:disable comments for legitimate patterns
- handle_call(:shutdown, _, state): split into a shutting_down=true
fast-path clause and a normal initiate_shutdown clause. No more
`if state.shutting_down` inside the callback body.
- terminate/2: extract graceful_shutdown_needed?/1 (four function
heads on the reason tag) and maybe_graceful_drain/2 (guarded on
state.shutting_down) so the shutdown side-effects are isolated to
a single, pattern-matched entry point.
Adds 4 unit tests for the pure callback paths
(shutting_down?, shutdown-already-in-progress, EXIT pass-through,
rescue fallback on unavailable GenServer).
