1. Problem

During host registration, `FactImporter#add_new_facts` inserts each new fact individually via `host.fact_values.create!` inside a loop. With 193 RHSM facts per registration, this produces 193 individual INSERT statements within a single transaction.

Under concurrent bulk registration (500-1000 hosts), this multiplies to hundreds of thousands of sequential INSERTs, significantly increasing database pressure and prolonging the critical `POST /rhsm/consumers` registration path.

1. Fix

For persisted hosts (where `host_id` is known), replace the per-fact loop with a single `FactValue.insert_all` call. The `host.new_record?` path is preserved as-is since bulk insert requires a host_id.

This reduces 193 individual INSERTs to a single statement per registration, consistent with how other bulk data is handled elsewhere in the codebase.