feat(js/core): added a way to run actions with side-channel data and streaming

[pavelgj]

    const act = action(
      {
        name: 'foo',
        inputSchema: z.string(),
        outputSchema: z.number(),
      },
      async (input, { sendChunk, context }) => {
        checkAuth(context);
        sendChunk(1);
        sendChunk(2);
        sendChunk(3);
        return input.length;
      }
    );

    const chunks: any[] = [];
    await act('1234', {
      context: { user: 'pavel' },
      onChunk: (c) => chunks.push(c),
    });

Checklist (if applicable):

• Tested (manually, unit tested, etc.)