Adding support for Mercusys MR90X

The non-linear progress feedback of the recovery option seems to be normal from as far as I remember.

The mr90x is not the easiest to install, if someone is unfamiliar with telnet and SSH, as it is not just uploading a firmware file.

We were not there, when you had installed it.
If you can be more specific about about the steps (from the installation steps from the OpenWRT wiki) you took to install it, potential error messages or command return messages and which exact binary you had used, there is a higher chance someone can help you.

So far I am suspecting that you missed some or all commands that you are supposed to run via SSH.