Starts the real Finch HTTP pool GgenIgniter.Finch (used by Tesla.Adapter.Finch,
configured in config/config.exs, for real HTTP calls made by
GgenIgniter.Query.Qlever and gno's SPARQL.Client) as part of the OTP
application boot -- so any real mix ggen_igniter.sync --engine qlever
invocation (a fresh process, not the test suite's own) has it available too.
Optionally also starts GgenIgniter.Controller (a persistent, BEAM-native
reconciliation GenServer -- see its own moduledoc) as a supervised, named
singleton (registered as GgenIgniter.Controller) -- OPT-IN ONLY, gated
behind Application.get_env(:ggen_igniter, :start_controller, false),
which DEFAULTS TO false. A library must never impose a persistent
process on every consumer by default; a consuming application that wants
the controller sets config :ggen_igniter, start_controller: true
explicitly. With the default false, existing consumers who only want the
CLI (mix ggen_igniter.sync) see zero behavior change from this child.