fix(qe): use ndmin=2 in np.loadtxt to handle single-line .evp files

[Copilot]

When Quantum Espresso cp.x trajectory files contain only a single timestep, the .evp energy file has just one data line. This caused np.loadtxt() to return a 1D array instead of the expected 2D array, leading to an IndexError when the code attempted 2D indexing operations.

# Before: This would fail with single-line .evp files
data = np.loadtxt(fname)  # Returns 1D array for single line
steps = []
for ii in data[begin::step, 0]:  # IndexError: too many indices for array
    steps.append("%d" % ii)

# After: Works consistently for both single and multi-line files  
data = np.loadtxt(fname, ndmin=2)  # Always returns at least 2D array
steps = []
for ii in data[begin::step, 0]:  # Works correctly
    steps.append("%d" % ii)

The fix uses numpy's ndmin=2 parameter to ensure the loaded data is always at least 2-dimensional, maintaining consistency between single-line and multi-line energy files without requiring additional reshaping logic.

Changes:

• Added ndmin=2 parameter to np.loadtxt() call in load_energy() function
• Added comprehensive test case to prevent regression

Testing:

• All existing QE tests continue to pass (63 tests)
• New test specifically validates single-line .evp file handling
• CLI functionality verified to work end-to-end

Fixes #899.

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[njzjz]

pre-commit.ci autofix

[codspeed-hq]

CodSpeed WallTime Performance Report

Merging #900 will not alter performance

_{Comparing copilot/fix-899 (e038715) with devel (7212c33)}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

✅ 2 untouched

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.06%. Comparing base (7212c33) to head (e038715).
⚠️ Report is 18 commits behind head on devel.

Additional details and impacted files

@@           Coverage Diff           @@
##            devel     #900   +/-   ##
=======================================
  Coverage   86.06%   86.06%           
=======================================
  Files          83       83           
  Lines        7886     7886           
=======================================
  Hits         6787     6787           
  Misses       1099     1099           

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[njzjz]

good