Extend slopesFF with last usable cell

Summary:

This is a fix for applying xray-cor. Before We were extending the SlopesFF constant with ones if it is a development SlopesFF with not all of (128, 512, < mem_cells) expected cells. But old constant is already of shape (128, 512, 2).

This MR introduces:

1. different expansion. AS it is better to use last usable memory cells for SlopesFF.

2. ff_gain, a conversion gain parameter that is used in case of absolute SlopesFF gain constant. Which is the case for the new FFs

Testing:

Retrieving SlopesFF from DB

xfel-calibrate AGIPD CORRECT \
--slurm-mem 750 \
--slurm-name cor_SPB_98 \
--karabo-da -1 \
--receiver-id {}CH0 \
--karabo-id-control SPB_IRU_AGIPD1M1 \
--karabo-da-control AGIPD1MCTRL00 \
--h5path-ctrl /CONTROL/{}/MDL/FPGA_COMP_TEST \
--overwrite --sequences-per-node 1 \
--in-folder /gpfs/exfel/exp/SPB/202030/p900119/raw/ \
--out-folder /gpfs/exfel/data/scratch/ahmedk/test/SPB_AGIPD2 \
--karabo-id SPB_DET_AGIPD1M-1 \
--run 98 --blc-stripes \
--rel-gain \
--adjust-mg-baseline \
--blc-set-min \
--xray-gain \
--force-hg-if-below \
--force-mg-if-below \
--low-medium-gap \
--zero-nans \
--zero-orange \
--sequences 0 \

Retrieving SlopesFF given local path

xfel-calibrate AGIPD CORRECT \
--slurm-mem 750 \
--slurm-name correct_MID_agipd_319 \
--karabo-id MID_DET_AGIPD1M-1 \
--karabo-id-control MID_EXP_AGIPD1M1 \
--karabo-da-control AGIPD1MCTRL00 \
--h5path-ctrl /CONTROL/{}/MDL/FPGA_COMP \
--overwrite \
--in-folder /gpfs/exfel/exp/MID/202030/p900137/raw/ \
--out-folder /gpfs/exfel/data/scratch/ahmedk/test/AGIPD_FF \
--slopes-ff-from-files /gpfs/exfel/d/proc/MID/202031/p900148/proc_vtst/cascella//FF/GAIN_MAPS/202cells2.2MHz.4p.lim1.gs0r319r322r324/ \
--run 319 \
--sequences 74 \
--modules 4 \

Reviewers:

@danilevc @kamile @jsztuk