ENH PiSSA/OLoRA: Preserve original config on save (#2077)
Resolves #2075
When saving PiSSA or OLoRA with the option to convert to normal LoRA,
the LoRA weight shapes change, which means that some values like r and
alpha need to be adjusted in the saved PEFT config. However, these
modifications should be limited to the saved config, while the loaded
config should stay the same.
This PR implements this change by creating a copy of the config before
modifying it.
