Efficient arithmetic operations in the IxVM

Very basic operations are defined in Lean in a way that will be very slow when run in the IxVM.

We need a way to turn those into native Aiur arithmetic operations.

The issue identifies Lean arithmetic definitions, the IxVM, and native Aiur arithmetic operations, but names no files, tests, or entry points. Start by locating the IxVM arithmetic execution path and the Lean definitions it handles. Done means the basic operations execute as native Aiur arithmetic rather than through the slower Lean implementation.

Written by the indexing model from the issue text.