refactor: unit testable units and cleaner dep injection

go/migrations/000015_particle_drop_network_fk.down.sql

@@ -0,0 +1,3 @@
+ALTER TABLE particles
+  ADD CONSTRAINT particles_network_id_fkey
+  FOREIGN KEY (network_id) REFERENCES networks(id) ON DELETE CASCADE;

go/migrations/000015_particle_drop_network_fk.up.sql

@@ -0,0 +1,2 @@
+ALTER TABLE particles
+  DROP CONSTRAINT IF EXISTS particles_network_id_fkey;