Summary:

**fix two bugs**

thanks go to pzhan9 for reporting these issues! (see D78298712)

(1) one in `reify_view` where views with strides were reified incorrectly. the old code assumed views could always be expressed as contiguous `range(start..start + len)` expressions, even when the view's stride differed from the base. this produced incorrect selections when the view was strided relative to the base layout.

the fix is to recognize when a view is layout-aligned; that is, when each of its strides is an integer multiple of the corresponding base stride, including the unitary case; and to reify such views using `Range(start, Some(end), step)` expressions that preserve both shape and layout. previously, only the unitary case (`step` = 1) was handled. this change extends support to non-unitary aligned views, such as `step` = 2, by correctly computing the step factor and corresponding end coordinate.

if any dimension is not layout-aligned — that is, if `view_stride` % `base_stride` ≠ 0 — we conservatively fall back to enumerating all selected coordinates explicitly.

(2) also fixes a bug in `Shape::select()` where the length of a strided range was computed using truncating division (symptom: a strided `select()` like `0..7 step 2` gives sizes: `[3]`, but the selected indices are clearly `[0, 2, 4, 6]` i.e. 4 elements). this now correctly uses ceiling division to ensure all selected indices are included.

Reviewed By: pzhan9

Differential Revision: D78315005