Add ChangePassword API method

Add support for changing the device password on an initialized BitBox02.

Changes:
- Add ChangePasswordRequest protobuf message to bitbox02_system.proto
- Add change_password field to Request oneof in hww.proto
- Implement ChangePassword() method in system.go
- Add firmware version check (requires v9.25.0+)
- Add status validation (device must be StatusInitialized)
- Add TestSimulatorChangePassword test coverage
- Regenerate protobuf Go files

The ChangePassword() method validates device state and firmware version
before initiating the password change workflow on the device.

Author: cedwies

api/firmware/messages/antiklepto.pb.go

@@ -66,3 +66,6 @@ message SetDeviceNameRequest {
 message SetPasswordRequest {
     bytes entropy = 1;
 }
+
+message ChangePasswordRequest{
+}