Make params prefix

[newville]

This should fix #893

Type of Changes

• Bug fix
• New feature
• Refactoring / maintenance
• Documentation / examples

Tested on

Python: 3.10.10 | packaged by conda-forge | (main, Mar 24 2023, 20:17:34) [Clang 14.0.6 ]
lmfit: 1.2.1.post5+g980a5d1, scipy: 1.10.1, numpy: 1.24.3, asteval: 0.9.30, uncertainties: 3.1.7

Verification

Have you

• included docstrings that follow PEP 257?

• referenced existing Issue and/or provided relevant link to mailing list?

• verified that existing tests pass locally?

• verified that the documentation builds locally?

• squashed/minimized your commits and written descriptive commit messages?

• added or updated existing tests to cover the changes?
• updated the documentation and/or added an entry to the release notes (doc/whatsnew.rst)?
• added an example?

[codecov]

Codecov Report

Merging #895 (aaf908e) into master (980a5d1) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #895   +/-   ##
=======================================
  Coverage   93.55%   93.55%           
=======================================
  Files          10       10           
  Lines        3615     3615           
=======================================
  Hits         3382     3382           
  Misses        233      233           

Impacted Files	Coverage Δ
lmfit/model.py	91.08% <100.00%> (ø)

[newville]

@reneeotten We're kind of stacking up a lot of PRs, and I am reluctant to let these linger too long and have PRs get out-of-date This one seems the least in need of discussion to me, so I'm going to merge it.