Support calibration of XTE data in event mode

[matteobachetti]

I had to change a little the structure, so that mission support is a separate beast than simple I/O.

• XTE/PCA is now supported with the recommended calibration. Science Event files from the XTE archive (those starting with SE and GX) can now be loaded in Stingray. More versions of files can be added later

• Calibration functions are moved to a separate mission_support module

• [x] Basic implementation

• [x] Working tests

• [x] Documentation on how to use this machinery

[pep8speaks]

Hello @matteobachetti! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file stingray/mission_support/rxte.py:

Line 283:31: E203 whitespace before ':' Line 284:34: E203 whitespace before ':'

Comment last updated at 2024-05-07 09:47:27 UTC

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.54%. Comparing base (ca74d3c) to head (800056b).

:exclamation: Current head 800056b differs from pull request most recent head 2896fa8. Consider uploading reports for the commit 2896fa8 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #816 +/- ## ========================================== + Coverage 96.50% 96.54% +0.03% ========================================== Files 45 48 +3 Lines 9149 9254 +105 ========================================== + Hits 8829 8934 +105 Misses 320 320 ```

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