Merge #1537

1537: Use static range in Grad setproperty! r=mwarusz a=mwarusz

# Description

After #1458 I noticed a slowdown. This PR proposes a fix.
Running ```julia --project=. experiments/AtmosLES/bomex_les.jl --monitor-timestep-duration 100steps``` I get
Before:
```
┌ Info: Wall-clock time per time-step (statistics across MPI ranks)
│    maximum (s) =    1.5273617989999998e-02
│    minimum (s) =    1.5273617989999998e-02
│    median  (s) =    1.5273617989999998e-02
└    std     (s) =                       NaN
```
After:
```
 Info: Wall-clock time per time-step (statistics across MPI ranks)
│    maximum (s) =    1.1554147779999999e-02
│    minimum (s) =    1.1554147779999999e-02
│    median  (s) =    1.1554147779999999e-02
└    std     (s) =                       NaN
```

The fix relies on unexported `StaticArrays` API but JuliaArrays/StaticArrays.jl#474 makes me think that this is ok.




Co-authored-by: Maciej Waruszewski <[email protected]>

Author: bors[bot]

src/Utilities/VariableTemplates/VariableTemplates.jl

@@ -309,7 +309,14 @@ end
             offset += 1
         elseif T <: StaticArray
             N = length(T)
-            retexpr = :(array[:, ($(offset + 1)):($(offset + N))] = val)
+            retexpr = :(
+                array[
+                    :,
+                    # static range is used here to force dispatch to
+                    # StaticArrays setindex! because generic setindex! is slow
+                    StaticArrays.SUnitRange($(offset + 1), $(offset + N)),
+                ] = val
+            )
             offset += N
         else
             offset += varsize(T)