Small issues remaing with frozen mode

I'm working on some multiproc tests right now.
There are still some wrong behavior with the frozen mode, when the output param is set during init.

Here is the typical workflow :

import os

os.environ["OTB_LOGGER_LEVEL"] = "WARNING"
import pyotb


img = "SENTINEL2A_20230502-104854-829_L2A_T31TEJ_NDVI.tif"

app = pyotb.BandMath([img], exp=f"im1b1 > {val}", out=f"/tmp/test_{val}.tif", frozen=True)

...

app.write(pixel_type = "uint8")

In the case we want to set path during init, but also the pixel type, this is failing because the pixel_type is ignored right now since we only set the pixel type during write for args passed to the write func.

I found the fix for this. Will push a MR soon.