Warn for explicit declaration of immutable params with units

[jsiirola]

Fixes #3002

Summary/Motivation:

#3002 pointed out that we silently force Params with units to be mutable, even when the user explicitly sets mutable=False. This PR adds a warning when we convert a Param that was explicitly immutable to being a mutable Param.

Changes proposed in this PR:

• Issue warning when Param is constructed with units and explicitly set to immutable.
• Test this behavior

Legal Acknowledgement

By contributing to this software project, I have read the contribution guide and agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the BSD license.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (bdbcb31) 88.10% compared to head (8967037) 88.08%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3004      +/-   ##
==========================================
- Coverage   88.10%   88.08%   -0.02%     
==========================================
  Files         769      769              
  Lines       89520    89526       +6     
==========================================
- Hits        78869    78863       -6     
- Misses      10651    10663      +12     

Flag	Coverage Δ
linux	85.18% <100.00%> (-0.01%)	⬇️
osx	74.99% <100.00%> (+<0.01%)	⬆️
other	85.36% <100.00%> (+<0.01%)	⬆️
win	82.43% <100.00%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
pyomo/core/base/param.py	82.07% <100.00%> (+0.28%)	⬆️

... and 2 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.