chore(main): release 6.4.0 #2028

Job	Run time
Test Python 3.10	7m 26s
Downstream import smoke (representative consumer symbols)	48s
AdCP storyboard runner — v3 reference seller (translator)	2m 34s
Validate schemas are up-to-date	21m 2s
AdCP storyboard runner — sales-proposal-mode (proposal_finalize)	1m 35s
AdCP storyboard runner — examples/multi_platform_seller (PlatformRouter)	1m 50s
Test Python 3.11	6m 46s
v3 reference seller — pytest (respx-mocked upstream)	42s
AdCP storyboard runner — examples/seller_agent.py (@adcp/sdk adcp-3.1)	2m 32s
AdCP storyboard runner — examples/seller_agent.py (@adcp/sdk adcp-3.0)	2m 12s
Test Python 3.12	6m 44s
Postgres conformance tests (Postgres 16)	1m 24s
Validate conventional commit format	-1s
Test Python 3.13	6m 23s
AdCP storyboard runner — examples/seller_agent.py	2s
	1h 1m 59s

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