Refactor the VM to use vec<u8> instead of current i64

[kennytheeggman]

In the refactor, also begin to develop the corresponding primitives for dynamically sized arrays and/or indirection, and specify them in the syntax productions tab in the doc: https://docs.google.com/document/d/1d__S2-pd7m7n79SpoF7bO-xeixnd5Xa-Ro201TB_meU/edit?tab=t.ny20qnyjvowd