RISC-V: Incorporate macro structs into re-usable struct

Closes RV-171

Review Advisory

src/riscv/lib/src/machine_state/csregisters/values.rs has almost entirely changed. I recommend reviewing the resulting file instead of the diff in the Changes tab.

What

Use a single configurable struct to contain CSR values.

Why

Resolves a small performance regression from !14177 (merged).

How

Replace the various CSR value structs (layout, placed, allocated, bound) into a single CSRValueF that can be parameterised appropriately. Methods to transform or select fields of this struct make other code locations simpler.

Manually Testing

make -C src/riscv all

Benchmarking

	master	This MR	Improvement
M3 MBP	0.365 TPS	0.365 TPS	0%
Benchmark Machine	0.136 TPS	0.138 TPS	1.5%

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.
• Benchmark performance and populate the table above if needed.
• 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.