Fix Rasters.create not respecting Extent with res (#1031)

## Summary - Fix off-by-one in `_extent2dims` when using `res` with `Intervals` sampling — the `res` path was missing the closed-interval boundary adjustment already present in the `size` path, causing an extra cell that overshoots the requested extent - Change 2 existing `@test_broken` to `@test` (now passing) - Add dedicated tests for `Start`, `End`, and `Center` locus with the exact reproduction case from #1031 Closes #1031 ## Test plan - [x] Verified `Rasters.create(Float64, Extent(X=(-180,180), Y=(-90,90)); res=1/12, sampling=Intervals(Start()))` produces size `(4320, 2160)` and extent `(-180, 180) x (-90, 90)` - [x] Verified same for `End` and `Center` locus - [x] Verified existing `@test_broken` cases now pass with correct extent and size 🤖 Generated with [Claude Code](https://claude.com/claude-code)