chore: modernise codebase for Java 17 baseline

[confuser]

Summary

Brings the codebase forward to take full advantage of the existing Java 17 toolchain bump and to remove a long tail of dependencies that no longer compile, build, or run cleanly.

This is mostly internal modernisation - no public-facing config or message keys change. User-visible runtime changes are documented in UPGRADE.md.

Changes

Test framework

• Migrated every test from JUnit 4 + PowerMock to JUnit 5 (Jupiter).
• Mockito 3.7.7 → 5.14.2; PowerMock dropped entirely.
• javafaker 1.0.2 → datafaker 2.5.4 (javafaker is unmaintained).
• hamcrest-library 1.2.1 → hamcrest 2.2; awaitility 4.0.1 → 4.3.0; mariaDB4j 2.6.0 → 3.3.1; jacoco 0.8.11 → 0.8.12.
• Added BasePluginDbTest.requireCommand(name) helper so command tests declare the assumption once in @BeforeEach instead of repeating Assumptions.assumeTrue(cmd != null) per @Test.

Runtime libraries

• HikariCP 6.3.3, ORMLite 6.1, MariaDB JDBC 3.5.7, MySQL Connector/J 8.4.0. H2 deferred to avoid an on-disk migration burden for existing users.
• DatabaseConfig.getJDBCUrl() now emits driver-specific JDBC URLs (sslMode for MariaDB 3.x; drops the deprecated disableMariaDbDriver flag for MySQL 8.x).
• SLF4J 1.x → 2.0.17 with a custom BanManagerSlf4jServiceProvider registered via META-INF/services. Bukkit shadowJar enables mergeServiceFiles() and relocates org.slf4j at task level so the ServiceLoader finds the relocated provider in the shaded JAR.
• SnakeYAML 2.x: LoaderOptions configured with allowDuplicateKeys=true, 32 MiB code-point limit and depth=100 to keep older user-edited YAML loading without surprises.
• bStats 3.2.1, PlaceholderAPI/Adventure refresh, Lombok 1.18.38.
• ORMLite logging is now scoped via Logger.setGlobalLogLevel on the shaded backend rather than the global LOCAL_LOG_LEVEL system property, so other plugins' ORMLite is unaffected.

Language idioms

• Plain DTOs converted to records: HistoryEntry, PlayerNameSummary, CommandInfo, Fetcher, UUIDFetcher, Hook, plus a unified Webhook record (replaces the previous WebhookHookConfig/WebhookData pair). Records use compact constructors for defensive copying of headers and pre/post hook lists.
• httpClient field is now volatile for the double-checked init in BanManagerPlugin; HTTP/2 is the JDK default so the explicit version builder call is dropped. getHttpClient() carries thread-safety javadoc.
• Pattern matching for instanceof, switch expressions in the SLF4J logger and RollbackSync, immutable factories (Set.of/List.of/Map.copyOf) where appropriate.
• New StorageUtils.toSqlException helper to wrap the broader Exception thrown by ORMLite 6.x AutoCloseable resources, used by MigrationRunner, PlayerHistoryStorage, PlayerWarnStorage and InfoCommand. MigrationRunner.getCurrentVersion now logs unexpected exceptions at WARNING.

Test stability

• IPUtilsTest swaps faker.internet().ipV6Address().replaceAll("0","") for a curated IPv6 sample set with canonical-form comparison; the previous random data occasionally produced invalid addresses.
• forkEvery=1 stays on (and is documented inline) because several tests leak static state - JDBC drivers, native handles, daemon executors - that hangs the suite in a single JVM.

Documentation

• New UPGRADE.md describing user-visible runtime changes (MariaDB JDBC scheme, MySQL Connector/J 8.x, SnakeYAML 2.x behaviour, bStats/PlaceholderAPI bumps, SLF4J 2.x on Bukkit).

Test plan

• ./gradlew :BanManagerCommon:test - 439 tests, 0 failures, 0 errors, 14 skipped (platform-specific *All commands not registered on common, same as before the assumeTrue refactor).
• Sequential ./gradlew build -x test produces every artifact across Bukkit, Bungee, Velocity, Sponge, and all 4 Fabric variants.
• CI (build.yml + e2e.yml) green across all e2e platforms (Bukkit, BungeeCord, Velocity, Sponge 1.20.6/1.21.1/1.21.3, Fabric 1.20.1/1.21.1/1.21.4/1.21.11).
• Smoke test on a real server for one of: MariaDB-backed install, MySQL-backed install (validates the new JDBC URL builder).

Companion PR

A matching modernisation PR will be opened against BanManager-WebEnhancer for its own dependency / JUnit 5 / Stonecutter sweep.