Github Actions Improvements

[darklight3it]

Issue #, if available:

N/A

Description of changes:

Fix multi-JDK test compatibility for UnsafeUtilTest and ClasspathLoaderTest in the Runtime Interface Client, and upgrade JUnit Jupiter from 5.9.2 to 5.14.3.

JUnit upgrade: 5.9.2 → 5.14.3.

CI workflow improvements:

• Restructured all 11 workflow files to follow "each workflow owns one module" philosophy with dependency-aware path triggers — when an upstream module changes, all downstream workflows trigger automatically.
• Added Maven dependency caching (actions/cache) to all workflows.
• Added workflow_dispatch to all workflows for manual triggering.

CI dependency graph for reference:

aws-lambda-java-core (no deps)
├── aws-lambda-java-log4j2
└── aws-lambda-java-runtime-interface-client (also depends on serialization)

aws-lambda-java-events (no deps)
├── aws-lambda-java-serialization
│   ├── aws-lambda-java-tests (also depends on events)
│   └── aws-lambda-java-runtime-interface-client (also depends on core)
├── aws-lambda-java-events-sdk-transformer
└── aws-lambda-java-tests (also depends on serialization)

samples (depends on events, serialization, tests)

Design principles:

• Each workflow builds and tests exactly one module.
• Each workflow triggers on changes to its own code and its upstream dependencies.
• No workflow builds downstream modules — that's the downstream workflow's job.
• All downstream workflows run in parallel when an upstream dependency changes.

Target (OCI, Managed Runtime, both):

Both

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.