react: add TransportProvider, make useClientTransport a context reader #120

Job	Run time
check	42s
test-integration node 24	58s
test node 24	47s
demo demo/vercel/react/use-chat	1m 17s
test node 20	45s
build	36s
demo demo/vercel/react/use-client-transport	1m 21s
test-integration node 20	1m 3s
test node 22	51s
test-integration node 22	1m 4s
	9m 24s

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