[TASK] Get IR for Rust Core

[iamrecursion]

Description

We need to be able to compile core to FLO, but currently we have no good way of getting it currently.

Spec

• Design our machine target.
• Work out how to build core for that target.
• Work out how to build core targeting IR for that target.
• Integrate a build step for this—or precompiled core—into the project build.
• Test the hieratika compiler with the target's datalayout and set it up to reject other layouts. Fix existing tests to comply.
• Run the hieratika compiler on the IR from core during the tests.
• Fix any bugs that arise.

[iamrecursion]

For easy reference:

• Core
• Custom targets
• Unstable build-std

[iamrecursion]

Had to do #118 to make this work, as the compiled version of core was compiled with LLVM 19.