RISC-V: support all branching instructions in JIT

Closes RV-505

What

JIT-support for all branching instructions.

Additionally, we give all branching instructions more explicit names - to help avoid the consistent issue of mistaking one for the other.

Would recommend reviewing commit by commit.

Why

Branching instructions appear throughout many blocks. The time spent between blocks (fetching a new one etc) is high, and therefore the JIT must support blocks which may branch (exiting the block) but in many cases also fall-through to the next instruction when the branching condition is not met.

How

We introduce two new functions: run_branch, run_branch_compare_zero taking a predicate for the comparison. Inlining reduces this all away for interpretation mode - indeed the output assembly for branching instructions is the same.

In the JIT, we insert a jump to the end, if the predicate condition holds - and otherwise we continue in what we call the 'fallthrough' block (where later instructions will continue to be lowered).

Manually Testing

make -C src/riscv all

Benchmarking

	master	This MR	Improvement
AMD 64 Linux	5.052 TPS	5.050 TPS	+0.2%
Benchmark Machine	3.805 TPS	3.811 TPS	-0.2%

Tasks for the Author

• Link all Linear issues related to this MR using magic words (e.g. part of, relates to, closes).
• Eliminate dead code and other spurious artefacts introduced in your changes.
• Document new public functions, methods and types.
• Make sure the documentation for updated functions, methods, and types is correct.
• Add tests for bugs that have been fixed.
• Put in reasonable effort to ensure that CI will pass.
  • make -C src/riscv
  • dune build src/lib_riscv
  • dune build src/rust_deps
• Benchmark performance and populate the table above if needed.
• Explain changes to regression test captures when applicable.
• Write commit messages to reflect the changes they're about.
• Self-review your changes to ensure they are high-quality.
• Complete all of the above before assigning this MR to reviewers.

Summary by CodeRabbit

• New Features

  • Enhanced branch operations now support a broader range of comparison conditions, including equality, inequality, and signed/unsigned tests.

• Bug Fixes

  • Improved handling of program counter updates based on new branching logic.

• Refactor

  • Streamlined control-flow logic by replacing legacy branch methods with more descriptive instruction names.

• Tests

  • Added comprehensive tests for branching scenarios, ensuring improved reliability under various conditions.