dont show 0.0 for parameter errors where no fitting was done

[rozyczko]

• Improved summary table clarity: Unfitted parameters now display an empty uncertainty cell rather than 0.0, preventing confusion between "no uncertainty" and "perfectly determined" values.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.69%. Comparing base (f96fefd) to head (e1baa8c).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #397   +/-   ##
========================================
  Coverage    93.69%   93.69%           
========================================
  Files           51       51           
  Lines         4519     4519           
========================================
  Hits          4234     4234           
  Misses         285      285           

Flag	Coverage Δ
integration	39.43% <0.00%> (ø)
unittests	93.69% <100.00%> (ø)

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Files with missing lines	Coverage Δ
src/easyreflectometry/summary/summary.py	90.40% <100.00%> (ø)

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