We now track in the lvalue whether what we computed is expected to be aligend or not, and then set some state in the memory system accordingly to make it (not) do alignment checks

Also enable some tests that were disabled for no apparant reason.
(The comment in zst.rs was wrong, the test was disabled also for miri execution.)
Delete env_args test as the args can actually be queried with MIR-libstd (currently, they are always empty)

This fixes the memory leaks when running a simple "Hello World" with MIR-libstd

Fixes #130.