UNOMI-892-maven-cache: Adopt Maven Build Cache, consolidate BUILDING into manual, update website docs

[sergehuber]

Title

UNOMI-892-maven-cache: Adopt Maven Build Cache and consolidate BUILDING into manual

Summary

Enables the Maven Build Cache for faster developer and CI builds and consolidates build documentation into the official manual to avoid duplication.

Why

• Faster feedback loops and reduced CI time.
• Single source of truth for build docs (easier to maintain).

Performance

• Without cache: ~1m59s (full clean install)
• With cache: ~3.176s (subsequent builds after initial)

What’s the Maven Build Cache (brief)

• Computes a key from project inputs; reuses outputs when inputs haven’t changed.
• If inputs change, modules rebuild normally (no correctness trade-off).
• Transparent to users: same Maven commands, faster when possible.
• Docs: Overview (https://maven.apache.org/extensions/maven-build-cache-extension/), Parameters (https://maven.apache.org/extensions/maven-build-cache-extension/parameters.html)

Safety and control

• Enabled by default via .mvn/maven-build-cache-config.xml (local cache only, no remote).
• Per-build controls:
  • Disable cache: -Dmaven.build.cache.enabled=false
  • Force rebuild (don’t read cache, still write results): -Dmaven.build.cache.skipCache=true
• Reset locally by deleting ~/.m2/build-cache (Windows: %USERPROFILE%\.m2\build-cache).

Documentation changes

• BUILDING now points to the manual: https://unomi.apache.org/manual/latest/index.html#_building
• Manual (manual/src/main/asciidoc/building-and-deploying.adoc):
  • Moved (and updated) all content that was in the BUILDING file to the manual
  • Added “Maven Build Cache” section with parameters, differences, purge/reset, and links.
  • Updated Maven requirement to 3.9.8.

Notable Maven cache configuration

• SHA-256 hashing.
• Inputs include src/; excludes pom.xml (version normalization) and src/main/javagen/**.
• Remote cache disabled.

[sergehuber]

Thanks for the approval @jayblanc !