feat(tci): the transmit meters, and no temperature invented

TX_POWER and TX_SWR are read-only commands the radio answers when asked,
so they are asked for on each poll of a KEYED radio and not at all
otherwise: a receiving station pays nothing for meters nobody is watching.
Both appear next to the S-meter only while transmitting, because showing
them the rest of the time would show the last thing that happened as if it
were now.

An SWR of 0 draws as '—' rather than as 1.0. A perfect match on an antenna
nobody has measured is the one reading an operator should never be handed.

There is no temperature. The protocol's command list has TX_POWER and
TX_SWR and nothing thermal at all — so rather than leave the question
hanging, it is written down where the next person will look for it. A
temperature invented from something else, on a transmitter, is exactly the
kind of number somebody would trust.

internal/cat/tci.go

@@ -304,6 +304,18 @@ func (t *TCI) ReadState() (RigState, error) {
 	} else {
 		st.FreqHz = t.freqA
 	}
+	// The transmit meters are asked for, not pushed: TX_POWER and TX_SWR are
+	// read-only commands the radio answers when asked, and asking is only worth
+	// anything while it is keyed. Fired and forgotten from here — the answers
+	// arrive on the reader like everything else — and only while transmitting,
+	// so a receiving station pays nothing for a meter nobody is watching.
+	if t.tx {
+		tx := t
+		go func() {
+			_ = tx.send("tx_power;")
+			_ = tx.send("tx_swr;")
+		}()
+	}
 	st.Mode = tciModeToADIF(t.mode, t.digitalDefault)
 	if st.FreqHz > 0 {
 		st.Band = BandFromHz(st.FreqHz)