[TOSA] Conv3d legalization

- Extend Torch to TOSA conversion with full aten.conv3d coverage,
  mapping padding/stride/dilation configs and bias handling into canonical TOSA conv ops.
- Refactor TorchToTosa lowering utilities to share more code between conv variants.
- Update conversion tests plus PT1 xfail lists to reflect the newly supported 3D convolution paths.

Signed-off-by: Cathal Corbett <[email protected]>
Change-Id: Iaf1261e121dec1ddb84b814e9058bb7ebadd4de7

Author: catcor01