fix(#328): close file handle in readDataFile using context manager

[Anirudh77715]

readDataFile used f.close without parentheses, meaning the file descriptor was never actually closed. Replaced with a with open() context manager that guarantees automatic closure.

Linked issue

• Closes [Bug] File handle not closed in readDataFile causing potential file descriptor leak #328

Existing related work reviewed

• Issues/PRs reviewed: None found after search

Overlap assessment

• Classification: none
• Overlapping items: none
• Why this is not duplicate/superseded: no existing PR addresses the unclosed file handle in readDataFile

Why this PR should proceed

Issue #328 documents a confirmed bug where f.close (without parentheses) is a no-op, causing file descriptor leaks under repeated calls. This PR applies the standard Python fix using a with context manager.

Summary

• What changed: Replaced bare f.close with with open() as f: context manager in readDataFile (API/Classes/Case/DataFileClass.py)
• Why: f.close without () is a no-op — the file is never closed, leaking OS file handles under repeated calls

Validation

• Tests added/updated (or not applicable)
• Validation steps documented
• Evidence attached (logs/screenshots/output as relevant)

Documentation

• Docs updated in this PR (or not applicable)
• Any setup/workflow changes reflected in repo docs

Scope check

• No unrelated refactors
• Implemented from a feature branch
• Change is deliverable without upstream OSeMOSYS/MUIO dependency
• Base repo/branch is EAPD-DRB/MUIOGO:main (not upstream)

Exception rationale