Remove watertap from required dependencies

[lbianchi-lbl]

• Add back MPI compatibility code that was left over during migration
• Modify parameter_sweep._compat so that get_solver() (from IDAES) is available even if watertap is not
  • The previous solution had an import watertap after the IDAES get_solver() import
  • This was to account for cases where watertap was available, but didn't have its own get_solver() implementation
  • However, this meant that the logic wouldn't work if only idaes, but not watertap, could be imported
  • The version proposed in this PR should now work in all cases:
    • If watertap.core.solvers exists: use get_solver() from WaterTAP
    • If watertap is not available, but IDAES is: use get_solver() from IDAES
    • If watertap is available, but doesn't have its own get_solver() (i.e. WaterTAP version preceeding Implement get_solver for WaterTAP watertap#1353): use get_solver() from IDAES, counting on the fact that the client code will import watertap, and therefore the global implicit WaterTAP solver settings will be applied to the solver returned by IDAES's get_solver()
• Add pytest.importorskip() for tests that use other watertap imports

[codecov]

Codecov Report

Attention: Patch coverage is 97.01493% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 94.33%. Comparing base (e9afcb3) to head (09a1162).

Files	Patch %	Lines
src/parameter_sweep/parallel/MPI/dummy_mpi.py	96.77%	1 Missing ⚠️
src/parameter_sweep/parameter_sweep.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #9      +/-   ##
==========================================
+ Coverage   94.24%   94.33%   +0.08%     
==========================================
  Files          33       36       +3     
  Lines        3649     3705      +56     
==========================================
+ Hits         3439     3495      +56     
  Misses        210      210              

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