v2.12.0

Major internal modernization. See CHANGELOG.md and release notes for full details.

Highlights:

• Replace spdlog/fmt with quill (lock-free async logging)
• Wrap all client code in namespace eonc
• Add PotRegistry singleton for structured force call tracking (_potcalls.json)
• Add SafeMath.h for FPE-safe arithmetic
• FPE hardening across 12 source files
• Metatomic ecosystem updates (torch 2.10, metatomic-torch 0.1.9+)
• Replace cxxopts with argum for CLI parsing