Show more digits of step size in progress_bar

[ricardoV94]

The two digits was copied from nutpie according to @jessegrabowski. I noticed that we always have a 0.0x, so it's not very useful. @aseyboldt explained that something something pymc nuts considers small eigenvalues of the matrix, while nutpie ignores it, which means our step-sizes tend to be smaller.

This PR adds one extra digit for me to look at.

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📚 Documentation preview 📚: https://pymc--7870.org.readthedocs.build/en/7870/

[jessegrabowski]

We might want to consider increasing the width of the Rich console, so we have a bit more real estate to show all these digits.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.90%. Comparing base (5d4c33c) to head (dda00cc).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7870      +/-   ##
==========================================
- Coverage   92.94%   91.90%   -1.05%     
==========================================
  Files         116      116              
  Lines       18845    18845              
==========================================
- Hits        17516    17319     -197     
- Misses       1329     1526     +197     

Files with missing lines	Coverage Δ
pymc/step_methods/hmc/nuts.py	97.61% <ø> (ø)

... and 3 files with indirect coverage changes

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[ricardoV94]

The width isn't dynamic?