Update to grobid 0.9.0

[lfoppiano]

This PR mostly updates libraries, including grobid:

• grobid 0.8.2 → 0.9.0 (core, trainer, service)
• Java 17 → 21 toolchain
• Gradle 7.2 → 9.0.0 wrapper
• Kotlin 1.8.21 → 2.0.21
• Shadow plugin migrated from the archived com.github.johnrengelman.shadow:7.1.0 to com.gradleup.shadow:8.3.10
• Dependency refresh matching parent grobid 0.9.x: Dropwizard 4.0.17, dropwizard-guicey 7.3.1, Jackson 2.21.1, Guava 33.5.0, commons-io 2.21.0, commons-lang3 3.20.0, JEP 4.3.1,
  JUnit BOM 5.14.1, EasyMock 5.6.0, MockK 1.13.17
• PowerMock 2.0.9 retained on Java 21 via --add-opens JVM flags (mirrors parent grobid's approach; Mockito migration tracked as deferred work)
• Gradle 9 compat fixes: JavaExec.main → mainClass, Report.enabled → Report.required, migrated to application { mainClass = ... } block (and corrected the stale
  GrobidSuperconductorsApplication reference to GrobidQuantitiesApplication)
• Docker / CI: builder image → eclipse-temurin:21-jdk-jammy, all 4 GitHub Actions workflows bumped to JDK 21, readthedocs → ubuntu-24.04
• Spelling: "occured" → "occurred" in exception messages across 8 source files
• Project version: 0.8.3-SNAPSHOT → 0.9.0-SNAPSHOT

[coveralls]

Coverage Report for CI Build 24136603630

Coverage decreased (-0.004%) to 34.674%

Details

• Coverage decreased (-0.004%) from the base build.
• Patch coverage: No coverable lines changed in this PR.
• 1 coverage regression across 1 file.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

1 previously-covered line in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
org/grobid/core/engines/utilities/LabellingUtils.kt	1	89.71%

---

Coverage Stats

Relevant Lines:	6401
Covered Lines:	2360
Line Coverage:	36.87%
Relevant Branches:	2972
Covered Branches:	890
Branch Coverage:	29.95%
Branches in Coverage %:	Yes
Coverage Strength:	1.5 hits per line

---

💛 - Coveralls