Consolidate GitHub Actions test workflow

Consolidate 4 separate platform jobs into single unified matrix-based job:
- Reduces workflow from 415 to 242 lines (42% reduction)
- Maintains identical test coverage across all platform/Java/config combinations
- Improves maintainability with single source of truth for test logic

Key improvements:
- Matrix-based platform configuration with include strategy
- Dynamic runner selection based on platform requirements
- Conditional OS setup consolidation (glibc vs musl, amd64 vs aarch64)
- Unified artifact collection with consistent naming
- Enhanced debugging with structured platform variables

Platform support preserved:
- glibc-amd64: Full Java matrix on ubuntu-latest
- musl-amd64: librca versions in Alpine container
- glibc-aarch64: ARM subset on arm-4core-linux runners
- musl-aarch64: ARM + Docker delegation to Alpine

All existing functionality maintained including Zing compiler restrictions,
container handling, Java version extraction, and failure reporting.

Author: jbachorik