Feat: Add roi_align_rotated

[DerrickUnleashed]

Adds ops_roi_align_rotated() / nn_roi_align_rotated(), a CPU RoI align pooling op for rotated boxes, ported from mmcv (Apache-2.0). Includes dispatcher + autograd kernels, R API + docs, and tests.

Closes #32

[DerrickUnleashed]

url <- "https://upload.wikimedia.org/wikipedia/commons/b/b6/Felis_catus-cat_on_snow.jpg"
arr <- base_loader(url)                           
input <- torch_tensor(arr)$permute(c(3, 1, 2))$unsqueeze(1)     

size <- get_image_size(input)
H <- size[2]/2; W <- size[1]/2
rois <- torch_tensor(matrix(c(
  0, 3*W/2, 3*H/2, W, H, pi,
  0, W/2,   3*H/2, W, H, pi,
  0, 3*W/2, H/2, W, H, pi,
  0, W/2,   H/2, W, H, pi
), ncol = 6, byrow = TRUE), dtype = torch_float32())

out <- ops_roi_align_rotated(input, rois, c(128, 128), spatial_scale = 1, sampling_ratio = 2)

grid <- vision_make_grid(out, num_rows = 2, padding = 6, pad_value = 1)

tensor_image_browse(grid)