Previously each OID was fetched individually, meaning 1000 OIDs
required 1000 round trips. Now OIDs are batched into groups of 60
(the SNMP max PDU size), reducing round trips by ~50x. Also
pre-sizes the OID value map to avoid repeated rehashing.
- Dockerfile: add BuildKit cache mounts for Go module and build caches,
pin both stages to Alpine 3.23
- CI: replace BUILDKIT_INLINE_CACHE with registry-based layer caching
(mode=max) for branch and release builds
- .dockerignore: exclude test files, Rust legacy, nix, and other
non-build artifacts from Docker context
- SNMP: lower MaxRepetitions from default 50 to 10 to prevent Mikrotik
routers from timing out during bulk walks
