Add support to re-estimate Smaps if trajectory changes during training

[chaithyagr]

We need a way to update the smaps internally while learning k-space trajectory. This can get complicated and it is worth starting a discussion on this.

Basically, we need a way to estimate and update Smaps internally in between forward.op, which is calibrationless fourier operator and fourier_op.adj_op, which is a self-calibrated fourier operator..