feat(gattc): add CanSendWriteWithoutResponse for darwin

[acouvreur]

bluetooth/gattc_darwin.go

Lines 200 to 208 in 5c61529

	// WriteWithoutResponse replaces the characteristic value with a new value. The
	// call will return before all data has been written. A limited number of such
	// writes can be in flight at any given time. This call is also known as a
	// "write command" (as opposed to a write request).
	func (c DeviceCharacteristic) WriteWithoutResponse(p []byte) (n int, err error) {
	c.service.device.prph.WriteCharacteristic(p, c.characteristic, false)
	return len(p), nil
	}

A limited number of such writes can be in flight at any given time.

We should be able to use CanSendWriteWithoutResponse in gattc_darwin.go to know if we can send another write without response command.

Otherwise, write without response commands are failing silently (maybe the WriteWithoutResponse command should call CanSendWriteWithoutResponse instead and fail if it returns false ?)

---

I'm not sure if this is relevant in other OS

---

Example usage:

for i = 0; i < total; i+=chunkSize {
	end := i + chunkSize
	if end > total {
		end = total
	}

	for !rx.CanSendWriteWithoutResponse() {
		// Wait until we can send more data
		println("Waiting to send data... CanSendWriteWithoutResponse=false")
		time.Sleep(10 * time.Millisecond)
	}

	_, err = rx.WriteWithoutResponse(buf[i:end])
	if err != nil {
		println("Failed to write to RX characteristic:", err.Error())
		return
	}
	fmt.Printf("Sent %d/%d bytes\r", end, len(buf))
}