fix(modbus-read): chunked reads + read timeout#16
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Some PLCs accept the TCP connection but reject a large read request, leaving the node hung with no error (verified: qty 2 works, qty 18 hangs on the same device). Add a `max_read` field: `quantity` is read in chunks of that size on the same connection and concatenated, so the whole block comes back without exceeding the device's per-request limit (0 = one request, unchanged default). Also bound each read with a 3s timeout so an unresponsive device surfaces an io_error and reconnects instead of hanging forever.
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Some PLCs accept the TCP connection but reject a large read request, leaving the node hung with no error (verified: qty 2 works, qty 18 hangs on the same device). Add a
max_readfield:quantityis read in chunks of that size on the same connection and concatenated, so the whole block comes back without exceeding the device's per-request limit (0 = one request, unchanged default). Also bound each read with a 3s timeout so an unresponsive device surfaces an io_error and reconnects instead of hanging forever.