chore: remove Mockito from test dependencies

[deer]

Removes Mockito from all modules that depended on it (base-configuration, base-flow, base-mereology, base-query, base-retryable) and replaces every mock with a hand-rolled test double or a simple inline lambda. The maven-dependency-plugin and maven-surefire-plugin build configuration that each module carried solely to wire Mockito as a -javaagent is removed as well, along with the root mockito.version property and its dependencyManagement entry.

Replacements: a TrackingSubscriber inner class in SubscriberRegistryTests captures subscription, items, completion, and error state in place of mock(Subscriber.class) + ArgumentCaptor; a shared NO_OP_SUBSCRIPTION constant stands in for mocked Subscriptions in FilteringSubscriberTests and MappingSubscriberTests; AtomicBoolean/AtomicInteger counters replace mocked suppliers and retryables in ConfigurationTests and BlockingRetryTests.