BUG - IDEX log_smooth_powerlaw and calibration file swap

[aldo9253]

Description of the issue

The calibration files were swapped in idex_l2a.py. A wrong variable was grabbed( m instead of k), and some units needed to be converted (pC - C). All around the log_smooth_power function.

aldo9253 working on the PR.

Steps to reproduce the issue

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Expected vs Actual behavior

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Code Snippet (If applicable)

Code

Additional notes, affected areas, and suggested fixes

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