feat(testing): make_request_context + build_asgi_app helpers #1170

Job	Run time
Postgres conformance tests (Postgres 16)	1m 3s
Validate schemas are up-to-date	3m 8s
AdCP storyboard runner — examples/seller_agent.py	1m 24s
AdCP storyboard runner — examples/multi_platform_seller (PlatformRouter)	1m 22s
v3 reference seller — pytest (respx-mocked upstream)	43s
Validate conventional commit format	6s
Downstream import smoke (representative consumer symbols)	27s
AdCP storyboard runner — v3 reference seller (translator)	1m 19s
Test Python 3.12	3m 15s
Test Python 3.11	3m 8s
Test Python 3.13	3m 14s
Test Python 3.10	3m 14s
	22m 23s

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