rename `SendMessagesRequestContext.id` to `chatId` #45

Job	Run time
test-integration node 24	59s
demo demo/vercel/react/use-chat	1m 29s
demo demo/vercel/react/use-client-transport	1m 29s
test-integration node 20	1m 12s
test-integration node 22	1m 9s
check	55s
test node 20	46s
test node 24	47s
build	39s
test node 22	44s
	10m 9s

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