* mem: add macro to assert on memory leak in scope
Implement `mem::@assert_leak` to assert on a memory leak in the scope of
the macro body. Memory report for the leak can be disabled by setting
the boolean argument to false.
* fix: add conditional compilation flags
* Moved the code into `mem.c3` and made it a builtin.
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Co-authored-by: Christoffer Lerno <christoffer@aegik.com>