LFVM: Refactor overflow checks, add tests (#838)

* Refactor overflow checks

delay range check for offset and length op parameters instead of doing at the beginning of the instructions to simplify instructions control flow.

* Apply review changes

Remove superfluous tests

* Apply review changes,

- remove dead code
-  move word cost after get slice to guard size cast
- move global variable to local scope
- fix variable naming

* Fix log broken test