Add a FinalizeExport RPC to pass the combined exporter response back to
the session provider after all exports complete. This lets clients run
completion work while the build's gateway references remain available.
Keep the callback optional for compatibility with existing session
exporters. Ignore unsupported finalization, propagate callback failures,
and support providers that only register a finalization callback.
Signed-off-by: Alberto Garcia Hierro <alberto.hierro@docker.com>
Move client integration test declarations out of the large harness files into
focused files for cache, exporters, sources, mounts, gateway behavior, and
related client features.
Keep registration lists grouped by source file, move non-gateway tests out of
the gateway harness, and remove the now-empty build_test.go. This is intended
as a mechanical split with no test logic changes.
Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
