Initialize mutable Params after DAE discretization

[mameikagou]

Fixes #4009.

Summary/Motivation:

DAE discretization adds points to a ContinuousSet after indexed Param components are constructed. Mutable Params with an explicit initializer therefore contain uninitialized ParamData at those new points.

Changes proposed in this PR:

• Initialize newly added indices of mutable Params from their existing initializer during DAE component expansion.
• Preserve lazy defaults, existing values, and immutable Param behavior.
• Add finite-difference and collocation regression coverage for scalar and indexed initializers.

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Notes for reviewers (optional): Verified the original reproducer before and after the change. The complete pyomo/dae/tests unittest suite passes: 178 tests, 33 skipped.

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[mrmundt]

With respect to code style and quality, this is great. Pending a review from another dev for mathematical correctness. (Probably @blnicho )

[codecov]

Codecov Report

❌ Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.14%. Comparing base (e099f64) to head (2328af6).

Files with missing lines	Patch %	Lines
pyomo/dae/misc.py	89.47%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4030      +/-   ##
==========================================
- Coverage   90.14%   90.14%   -0.01%     
==========================================
  Files         917      917              
  Lines      109261   109278      +17     
==========================================
+ Hits        98494    98507      +13     
- Misses      10767    10771       +4     

Flag	Coverage Δ
builders	29.11% <5.26%> (-0.01%)	⬇️
default	86.14% <89.47%> (?)
expensive	35.09% <5.26%> (?)
linux	87.68% <89.47%> (-1.98%)	⬇️
linux_other	87.68% <89.47%> (+<0.01%)	⬆️
oldsolvers	28.05% <5.26%> (-0.01%)	⬇️
osx	83.12% <89.47%> (+<0.01%)	⬆️
win	85.43% <89.47%> (-0.01%)	⬇️

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