Speed-up plotting routines

Description

Implement parallel plotting via multiprocessing for the DAC scans and S-bit rate scan analysis routines.

Related Issue

Fixes #37 (closed).

How Has This Been Tested?

Taking example input files available in /gemdata/data/dac-scan-in-2022081701 and /afs/cern.ch/work/c/cgalloni/public/4Yechan/ for the DAC scans and /gemdata/data/sbit-rate-scan-in-inductionOffHVstandby-2022110801 for the S-bit rate scan.

The changes were tested by running:

gemos analyze dac dac-scan-in-2022081701/fed146* test_dac1/ -m 4Yechan/vfat_map.dat -c 4Yechan/vfat_calibration.txt -p always

gemos analyze sbit sbit-rate-scan-in-inductionOffHVstandby-2022110801/fed1467-slot* test1_sbit/ -p 

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.