[Fix] Improve HTTP map interval logic for cache validation

[Fix] Improve HTTP map interval logic for cache validation

Properly differentiate between maps with and without cache validation:
- With ETag/Last-Modified: use 4x multiplier (cheap conditional requests)
- Without cache validation: enforce strict 10 minute minimum
- Add overflow protection for interval multiplication
- Actually use has_etag/has_last_modified parameters

This avoids overly aggressive slowdown (120x -> 4x) for maps with cache
validation while still preventing abuse of maps without validation.