Resolve dill incompatibility with attempt_import.

[jsiirola]

Fixes #2414

Summary/Motivation:

Current dill implementations look for the dill module by looking for the _dill attribute on all objects in the globals(). This was causing missing modules (ModuleUnavailable objects) to raise a DeferredImportError. This adds a special case to that this behavior does not trigger the DeferredImportError (and instead raises the "expected" AttributeError.

This also makes the ModuleUnavailable and DeferredImportModule classes picklable.

Changes proposed in this PR:

• Do not trigger a DeferredImportError when attempting to retrieve a _dill attribute
• Make ModuleUnavailable and DeferredImportModule classes picklable.

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

Merging #2419 (bedc0ef) into main (42ce167) will increase coverage by 1.48%.
The diff coverage is 50.00%.

❗ Current head bedc0ef differs from pull request most recent head 297f948. Consider uploading reports for the commit 297f948 to get more accurate results

@@            Coverage Diff             @@
##             main    #2419      +/-   ##
==========================================
+ Coverage   84.41%   85.89%   +1.48%     
==========================================
  Files         617      617              
  Lines       76183    76192       +9     
==========================================
+ Hits        64309    65448    +1139     
+ Misses      11874    10744    -1130     

Flag	Coverage Δ
linux	82.63% <50.00%> (+22.93%)	⬆️
osx	72.86% <50.00%> (?)
other	82.82% <50.00%> (+23.13%)	⬆️
win	79.64% <50.00%> (?)

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

Impacted Files	Coverage Δ
pyomo/common/dependencies.py	97.03% <50.00%> (-1.44%)	⬇️
pyomo/contrib/pynumero/sparse/block_matrix.py	89.96% <0.00%> (+0.16%)	⬆️
pyomo/solvers/plugins/solvers/gurobi_direct.py	71.91% <0.00%> (+0.16%)	⬆️
pyomo/core/expr/logical_expr.py	88.30% <0.00%> (+0.23%)	⬆️
pyomo/contrib/interior_point/interior_point.py	95.03% <0.00%> (+0.26%)	⬆️
pyomo/solvers/plugins/solvers/GUROBI.py	88.52% <0.00%> (+0.32%)	⬆️
pyomo/contrib/pynumero/sparse/block_vector.py	86.86% <0.00%> (+0.35%)	⬆️
pyomo/core/base/expression.py	90.04% <0.00%> (+0.49%)	⬆️
pyomo/core/base/units_container.py	98.08% <0.00%> (+0.54%)	⬆️
... and 43 more

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[mrmundt]

@jsiirola - I'll look into resolving the failing tests. I know you're busy today.

[jsiirola]

@mrmundt, I was just working in it. I think I just pushed a valid change that should fix the pickle issue.

[mrmundt]

The failing tests are now all passing. I will merge the PR.