Unstable DOS test

The test_dos_magnitude in test_dos.py is very unstable to any updates in the DOS and hard to recalibrate. This has been noticed by @pizarroj too. Rather than comparing the mean DOS of all non-zero values between 3 main codes. I suggest updating it to comparing the integral of the DOS. For now this can just remain the regular DOS and later be extended to include the normalized version.