additivity of timing

Timing is not additive if memory is allocated:

```
i3 : timing sum apply (100, i -> first timing (10000000:0))

o3 = 7.5996
-- 14.4016 seconds
```

Find out why.

No source files or tests are named. Start by reproducing the `timing sum apply` example with memory allocation, then trace how timing is measured and accumulated. Done means identifying why the reported timings are not additive and documenting the relevant cause or required correction.

Written by the indexing model from the issue text.