Move the cross-file integration fixtures — the service constructors
(newGameService/newSocialService/newRobotService/newMatchmaker), the game-assembly
helpers (newMirror/newGameWithSeats/newDraftGame), account provisioning
(provisionAccount/provisionGuest) and the stats reader — out of the domain test
files (newGameService alone was used by 10 files) into a single
backend/internal/inttest/helpers.go. Helpers used by a single file stay local.
Pure relocation: the helper bodies are unchanged, no test logic changes; the
imports the moves left unused are pruned. go vet -tags=integration is clean.
Ilia Denisov