Make machine-readable numeric formatting locale-independent - #3431

Summary

• use Locale.ROOT for TREC rows, generated document IDs, shard filenames, numeric TSV exports, test URLs, and generated documentation
• replace tests that forced Locale.US with regression coverage under mzn-Arab-IR and de-DE
• restore every temporary default-locale change in finally

Testing

• mvn -B clean package -Dslf4j.internal.verbosity=WARN with Temurin 21 on Ubuntu: 1,162 tests passed
• targeted locale-related suite: 83 tests passed
• documentation generation: 12 tests passed under each locale, with identical SHA-256 hashes for all 780 generated files
• git diff --check

Fixes #3427