Improve: Improve ci-loader

[lokidundun]

Purpose of the PR

• close [Improve][CI] Avoid repeated environment downloads in loader-ci #723

Main Changes

1. .github/workflows/loader-ci.yml

• Migrated MySQL to GitHub Actions services: Adopted the official mysql:5.7 container service with health check configured. This eliminates the need to execute docker pull and docker run for every workflow run.
• Added Hadoop caching: Cached ~/hadoop-2.8.5.tar.gz with a fixed cache key hadoop-2.8.5.
• Added HugeGraph Server caching: Cached ~/hugegraph-cache-${{ env.COMMIT_ID }}; the cache key contains the commit ID to enable auto-invalidation when the version changes.
• Removed the invocation of install-mysql.sh: MySQL is now provisioned by GitHub Actions services.

2. hugegraph-loader/assembly/travis/install-hadoop.sh

• Added local installation & cache validation: Skip re-download/extraction if /usr/local/hadoop already exists; use the cached tar.gz file directly if it exists (while the local directory is missing) to avoid repeated downloads from archive.apache.org.
• Added writes to GITHUB_ENV: Ensure subsequent steps can correctly obtain HADOOP_HOME and PATH environment variables.
• Made configuration writes idempotent: Only write core-site.xml and hdfs-site.xml if the configuration files do not exist or their content is mismatched.

3. hugegraph-loader/assembly/travis/install-mysql.sh

• Added idempotent check: Directly skip docker pull and docker run if the mysql:5.7 container is already running (e.g., provided by GitHub Actions services).

4. hugegraph-loader/assembly/travis/install-hugegraph-from-source.sh

• Added build caching: Check if the packaged apache-hugegraph-*.tar.gz exists in ~/hugegraph-cache-${COMMIT_ID} before building. Use the cached tarball directly and skip the time-consuming git clone + mvn package if it exists; copy the tarball to the cache directory for reuse in future runs after the build if it does not exist.

Verifying these changes

• Trivial rework / code cleanup without any test coverage. (No Need)
• Already covered by existing tests, such as (please modify tests here).
• Need tests and can be verified as follows:
  • xxx

Does this PR potentially affect the following parts?

• Nope
• Dependencies (add/update license info)
• Modify configurations
• The public API
• Other affects (typed here)

Documentation Status

• Doc - TODO
• Doc - Done
• Doc - No Need