No backward pass for RmsNorm if tensor is contiguous

[agerasev]

RmsNorm switches to faster implementation if tensor is contiguous:

candle/candle-nn/src/layer_norm.rs

Lines 174 to 175 in 82b641f

	if xs.is_contiguous() {
	crate::ops::rms_norm(xs, &self.0.weight, self.0.eps as f32)

But it does not support backward pass:

candle/candle-nn/src/ops.rs

Line 640 in 82b641f

xs.apply_op2_no_bwd(alpha, &RmsNorm { eps })

Maybe it's better to implement ModuleT rather than Module for RmsNorm and use faster implementation only if train == false?