IntelProvider is async-first (every concrete provider does HTTP), bounded
by a per-provider asyncio.Semaphore, and contractually never raises —
errors land in IntelResult.error so a single provider's outage doesn't
poison the worker pass for an entire IP.
Factory returns a list (not a singleton like geoip) because intel
enrichment fans out across all enabled providers per IP, with row-level
partial-success handling. Lazy imports keep the module dependency-free
when intel is disabled.
Concrete providers (greynoise/abuseipdb/feodo/threatfox) land in
follow-up commits — factory references them via lazy import so tests
covering the disabled and unknown-name paths pass on their own.
