The codelinter complains about unused variables in ESP-IDFs framework code. You can safely ignore that which does not come from your code.
You put your upload baud at 115200 (approx. bits per second), which is slow when you want to upload ~410 kilobytes 
Depending on the USB-to-serial chip on your devboard you can safely increase the upload_speed in your platformio.ini to e.g. 460800 (for common baudrates see here).
This is an error within Visual Studio code, see the thread In VSC Task Window always popping up: "Error: No handler found" - #48 by mrred128.