Do conversions tests

[shreyannandanwar]

New tests cover:

• character inputs silently coerced to NULL (legacy fallback)
• skip logic when input path exists and force is NULL
• force flag overrides skip logic
• empty inputs list returns settings unchanged
• reads pecan.METProcess.xml when needsave is FALSE

Tests added

Test	Why
character inputs → NULL	character inputs being silently coerced to NULL (legacy fallback)
skip when path exists + force is NULL	skip logic when an input already has a path and force is NULL
no skip when force is set	force flag overriding the skip logic
empty inputs list → no XML written	empty inputs list returning settings unchanged
reads pecan.METProcess.xml via empty inputs	reading pecan.METProcess.xml via the empty-inputs entry path

Notes

• No production code was changed, tests only
• Tests 4 and 5 are intentionally paired — they pin both
  sides of the path/force branch condition together
• Tests 1 and 7 both cover the XML read path but via
  different entry conditions, confirming the behavior is
  robust across routes into that branch

Review Time Estimate

• Immediately
• Within one week
• When possible

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• My name is in the list of CITATION.cff
• I agree that PEcAn Project may distribute my contribution under any or all of
  • the same license as the existing code,
  • and/or the BSD 3-clause license.
• I have updated the CHANGELOG.md.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.