Enable pre-heat for PMSx003 sensors

The PMSA003 sensor takes approximately 10 seconds to warm up, with
InconsistentObservation and WrongMessageFormat exceptions raised for
earlier samples. From experimentation, 10 seconds is almost exactly
the warm up time, but the datasheet actually recommends 30s [^1]:

    Stable data should be got at least 30 seconds after the sensor wakeup from the sleep mode because of the fan’s performance.

However, it makes sense to set this number based on what happens in
practice; we can always increase if others observe worse behaviour.

[^1]: https://cdn.shopify.com/s/files/1/0176/3274/files/PMSA003_datasheet.pdf?v=1619703

src/pms/sensors/plantower/pmsx003.py

@@ -13,6 +13,7 @@
 
 ALIASES = ("PMS1003", "G1", "PMS5003", "G5", "PMS7003", "G7", "PMSA003", "G10")
 
+PREHEAT = 10  # 10 seconds
 
 commands = base.Commands(
     passive_read=base.Cmd(b"\x42\x4D\xE2\x00\x00\x01\x71", b"\x42\x4D\x00\x1c", 32),