feat: added RIT and XIT for Icom

internal/cat/cat.go

@@ -382,6 +382,10 @@ type IcomTXState struct {
 	SMeter       int  `json:"s_meter"` // 0-100 (raw 0-255; S9≈120)
 	PowerMeter   int  `json:"power_meter"` // 0-100 (TX Po)
 	SWRMeter     int  `json:"swr_meter"`   // 0-100 (TX SWR)
+	// RIT / ΔTX (XIT).
+	RITHz int  `json:"rit_hz"` // RIT/XIT offset, signed Hz
+	RITOn bool `json:"rit_on"`
+	XITOn bool `json:"xit_on"`
 	// Set controls.
 	RFPower int `json:"rf_power"` // 0-100 (TX output)
 	MicGain int `json:"mic_gain"` // 0-100
@@ -422,6 +426,9 @@ type IcomController interface {
 	SetScope(bool) error     // enable/disable the spectrum-scope waveform stream
 	SetScopeMode(bool) error // true = fixed span, false = center-on-VFO
 	ScopeData() ScopeSweep   // latest assembled sweep (empty until enabled)
+	SetRIT(int) error        // RIT/ΔTX offset in signed Hz
+	SetRITOn(bool) error     // RIT on/off
+	SetXITOn(bool) error     // ΔTX (XIT) on/off
 }
 
 // ScopeSweep is one complete spectrum-scope sweep reassembled from the Icom's