chore: modernise build and tests for Java 17 baseline

[confuser]

Summary

Companion to BanManager PR #1070.

Modernises the build and remaining tests for the Java 17 baseline that's already in use, refreshes a few outdated dependencies, and unifies the bStats versions across platforms.

Changes

Build

• Stonecutter 0.7.11 → 0.8.3 (settings.gradle.kts uses the renamed shared.version() API instead of vers()).
• Foojay toolchain resolver 0.9.0 → 1.0.0.
• Added com.vanniktech.maven.publish to buildSrc so libs/sub-projects can publish consistently with BanManager.
• Set Libs sourceCompatibility/targetCompatibility and the TargetJvmVersion attribute to 17 (matches the Java 17 baseline already in use by other modules).
• Lombok 1.18.36 → 1.18.38.
• bStats Bukkit/Bungee/Velocity/Sponge unified at 3.2.1 (was a mix of 2.2.1 / 3.0.0 / 3.0.2).
• Guava 17.0 → 33.4.8-jre and dropped the unused bcpkix-jdk15on shade (only bcprov is referenced by the Argon2 encoder).
• Append -XX:+UseStringDeduplication to the Gradle JVM args.

Tests

• Migrated the three remaining tests (PlayerPinDataTest, CommonPlayerDeniedListenerTest, Argon2PasswordEncoderTest) from JUnit 4 + PowerMock + Mockito 4 to JUnit 5 + Mockito 5 (mockito-junit-jupiter 5.14.2). PowerMock dropped.
• mariaDB4j 2.6.0 → 3.3.1, awaitility 4.0.1 → 4.3.0, jacoco 0.8.11 → 0.8.12.
• Refreshed the forkEvery=1 inline comment to point at the BanManager common build for full rationale (JDBC drivers and native fixtures leak across runs).

Test plan

• ./gradlew :BanManagerWebEnhancerCommon:test - 22 tests, 0 skipped, 0 failures, 0 errors.
• Sequential ./gradlew build -x test produces every artifact across Bukkit, Bungee, Velocity, Sponge, and all 4 Fabric variants (1.20.1, 1.21.1, 1.21.4, 1.21.11).
• CI (build.yml + e2e.yml) green.
• Smoke test on a real server alongside the BanManager modernisation PR (validates the SLF4J/HikariCP/MariaDB/MySQL upgrades over there don't regress WebEnhancer's pin/web flows).

Notes

• The companion BanManager PR carries the bigger lift (HikariCP/ORMLite/JDBC driver upgrades, SLF4J 2.x, full JUnit 5 sweep across 67 test classes, DTOs to records). This PR is intentionally narrow.