added RX90 native gate and modified R method

[ElStabilini]

I added RX90 as native gate to be able to calibrate this gate separately from the RX gate

Checklist:

• Reviewers confirm new code works as expected.
• Tests are passing.
• Coverage does not decrease.
• Documentation is updated.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 50.91%. Comparing base (eca774d) to head (88d0fd1).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
src/qibolab/_core/native.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1103      +/-   ##
==========================================
+ Coverage   50.87%   50.91%   +0.03%     
==========================================
  Files          63       63              
  Lines        2905     2909       +4     
==========================================
+ Hits         1478     1481       +3     
- Misses       1427     1428       +1     

Flag	Coverage Δ
unittests	50.91% <75.00%> (+0.03%)	⬆️

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