Fix compute rms

[matteobachetti]

• [x] Make the code for rms computation a little more clear
• [x] deprecate old behavior
• [x] Check documentation --> Small update to Spectral Timing Exploration notebook

I also had to fix a couple of things related to warnings, because the new pytest is much pickier. All the changes to warnings (and to imports in the top of files) are due to that. Please ignore for the sake of this PR. Only consider changes to (test_)crossspectrum, powerspectrum, fourier, and minor related changes in multitaper, lombscargle and deadtime.

Resolve #790

[codecov[bot]]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (6f38ba2) 78.98% compared to head (02fe583) 95.83%.

:exclamation: Current head 02fe583 differs from pull request most recent head 10764e4. Consider uploading reports for the commit 10764e4 to get more accurate results

Files	Patch %	Lines
stingray/crossspectrum.py	87.50%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #792 +/- ## =========================================== + Coverage 78.98% 95.83% +16.84% =========================================== Files 43 43 Lines 8762 8784 +22 =========================================== + Hits 6921 8418 +1497 + Misses 1841 366 -1475 ```

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[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/tests/test_lightcurve.py:

Line 1713:101: E501 line too long (101 > 100 characters) Line 1734:101: E501 line too long (101 > 100 characters)

Comment last updated at 2024-01-29 14:44:59 UTC