Fix grid size

[CyprienBouton]

Change apply_grappa_kernel in src/ggrappa/application.py to return a kspace of the same size and fix issues related to kspace shape:

• line 80-82 uncomment to have the same grid size
• line 87 and 88 y_ival=range(shift_y, rec.shape[1], tbly*batch_size) when sbly=1 and z_ival = np.arange(0, rec.shape[2], sblz) when sblz=1
• line 98 fix zival to have values within z_ival

[mbertrait]

LGTM 👍