feat: mypy 1.16

[kerberizer]

As discussed, we have some problems with mypy 1.16, while 1.15 works fine. The changes in 1.16 are documented here. The error messages are here. No need to hurry with this, but would be helpful to have it fixed nonetheless.

  mypy: commands[0]> mypy src tests
  src/ramanchada2/io/experimental/read_txt.py:50: error: Value of type "tuple[str, ...] | None" is not indexable  [index]
  src/ramanchada2/io/experimental/read_txt.py:51: error: Value of type "tuple[str, ...] | None" is not indexable  [index]
  src/ramanchada2/spectrum/spectrum.py:38: error: Incompatible types in assignment (expression has type "ndarray[tuple[int, ...], dtype[floating[Any]]]", variable has type "ndarray[tuple[int, ...], dtype[float64]]")  [assignment]
  src/ramanchada2/spectrum/spectrum.py:138: error: Incompatible types in assignment (expression has type "ndarray[tuple[int, ...], dtype[float64]]", variable has type "None")  [assignment]
  src/ramanchada2/spectrum/spectrum.py:139: error: "None" has no attribute "flags"  [attr-defined]
  src/ramanchada2/spectrum/spectrum.py:157: error: Incompatible types in assignment (expression has type "ndarray[tuple[int, ...], dtype[float64]]", variable has type "None")  [assignment]
  src/ramanchada2/spectrum/spectrum.py:158: error: "None" has no attribute "flags"  [attr-defined]
  src/ramanchada2/spectrum/calibration/scale_xaxis.py:56: error: Incompatible types in assignment (expression has type "float", variable has type "ndarray[tuple[int, ...], dtype[float64]]")  [assignment]
  Found 8 errors in 3 files (checked 160 source files)