✨ PwOutput: Add fermi_energy_up and fermi_energy_down

Parse the spin-up and spin-down Fermi energies from the XML `two_fermi_energies`
element for spin-polarized calculations (`tot_magnetization` set in `SYSTEM`). Values
are converted from Hartree to eV, consistent with `fermi_energy`.

Adds a `tot_magnetization` test fixture (QE v7.5) with a cleaned-up stdout following
the fixture cleanup convention.

Author: mbercx

src/qe_tools/outputs/pw.py

@@ -81,6 +81,28 @@ class _PwMapping:
     )
     """Fermi energy in eV."""
 
+    fermi_energy_up: float = Spec(
+        (
+            "xml.output.band_structure.two_fermi_energies",
+            lambda energies: energies[0] * CONSTANTS.hartree_to_ev,
+        )
+    )
+    """Fermi energy of spin-up channel in eV.
+    
+    Only available when ``tot_magnetization`` is set in ``SYSTEM``.
+    """
+
+    fermi_energy_down: float = Spec(
+        (
+            "xml.output.band_structure.two_fermi_energies",
+            lambda energies: energies[1] * CONSTANTS.hartree_to_ev,
+        )
+    )
+    """Fermi energy of spin-down channel in eV.
+    
+    Only available when ``tot_magnetization`` is set in ``SYSTEM``.
+    """
+
     total_energy: float = Spec(
         (
             "xml.output.total_energy.etot",