Fix error in imi_preview for estimating computing cost and averaging kernel sensitivity

[1Dandan]

Name and Institution (Required)

Name: Dandan Zhang
Institution: Harvard University

Describe the update

• In imi_preview.py, the inversion area cannot be calculated correctly with the function used there. Instead, an alternate method of estimating number of grid box is used as implemented in src/inversion_scripts/imi_preview.py. This will fix the error stated in Potential bugs for the calculation for averaging kernel sensitivity and cost estimation in preview? #331 for the cost estimation in imi_preview.py.
• Fix the error for calculating averaging kernel density as well as stated in Potential bugs for the calculation for averaging kernel sensitivity and cost estimation in preview? #331.
• Additionally, the message printed out for TROPOMI file time range would be one day more, and thus confusing. Fix it accordingly.