fix: tie query()/read() host timeout to the controller's read_tmo_ms

Found against real hardware: a fixed 2.0s host-side read timeout was
shorter than the device's configured read_tmo_ms (3000ms). The
controller keeps a "++read" outstanding internally until EOI or its
own timeout, so the client gave up and sent the next command first --
that command's reply then got lost/delayed behind the still-pending
read, surfacing as a spurious TransportTimeout on the *following* call
(observed: query("*IDN?") timed out as expected with no instrument
attached, then srq() right after it timed out too, on a device with
read_tmo_ms=3000).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

progpib/controller.py

@@ -7,7 +7,7 @@ from .exceptions import CommandError
 from .transport import EthernetTransport, SerialTransport, Transport
 
 _DEFAULT_COMMAND_TIMEOUT = 1.0  # seconds, for ++cmd query replies
-_DEFAULT_READ_TIMEOUT = 2.0  # seconds, for ++read / query() instrument data
+_READ_TIMEOUT_MARGIN = 0.5  # seconds, added on top of read_tmo_ms (see _instrument_read_timeout)
 
 
 class GpibController:
@@ -59,6 +59,22 @@ class GpibController:
         if self.mode != 0:
             raise CommandError(f"++{command_name} is only valid in DEVICE mode")
 
+    def _instrument_read_timeout(self, explicit: float | None) -> float:
+        """Host-side timeout for reading instrument data.
+
+        Must be longer than the controller's own `read_tmo_ms`: the
+        controller keeps a "++read" outstanding internally (waiting for
+        EOI or its own timeout) before it will process the next command,
+        so a shorter host-side timeout gives up and sends the next command
+        while the controller is still finishing the previous read -- that
+        reply then arrives late and gets mistaken for the next command's
+        reply (or times out entirely). Costs one extra round trip when the
+        caller doesn't pass an explicit timeout; pass one to skip it.
+        """
+        if explicit is not None:
+            return explicit
+        return (self.read_tmo_ms / 1000.0) + _READ_TIMEOUT_MARGIN
+
     # -- config properties ------------------------------------------------
 
     @property
@@ -260,7 +276,7 @@ class GpibController:
                 raise ValueError("terminator char must be between 0 and 255")
             command = f"read {char}"
         self._send_command(command)
-        return self._transport.read_until_quiet(timeout=timeout or _DEFAULT_READ_TIMEOUT)
+        return self._transport.read_until_quiet(timeout=self._instrument_read_timeout(timeout))
 
     # -- raw instrument I/O ---------------------------------------------
 
@@ -280,4 +296,4 @@ class GpibController:
         """
         self.write(data)
         self._send_command("read eoi")
-        return self._transport.read_until_quiet(timeout=read_timeout or _DEFAULT_READ_TIMEOUT)
+        return self._transport.read_until_quiet(timeout=self._instrument_read_timeout(read_timeout))