Refactor: charge_mixing

[Qianruipku]

move functions in mixing to cpp files
Before: only one mixing_beta can be used for this mixing
After: We can define any form of mixing_beta function.
Add UTs for double_grid
fix different charge_mixing reults of USPP (NSPIN = 2) because the global varibal in mixing of #3226
Change time out to 1600 s

Update results by #2998 mentioned in #3242
The results changed because:

1. the memory of rho is changed from rho[is][nrxx] to rho[ns*nrxx]
2. ndim = 7 in LCAO is changed to ndim = 8

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[WHUweiqingzhou]

Thanks for your effort! This refactor is helpful for the implementation of new mixing method.

[hongriTianqi]

@Qianruipku This PR does not reduce the number of Warnings.