RISC-V: inline parser & split cache paths for compressed/uncompressed

Relates to RV-172

What

Inline the parser into fetch_instr and write to the instruction cache on separate paths for compressed vs uncompressed instructions.

Why

Doing so allows the elimination of a check on the cache_uncompressed path. We do not allow caching of an instruction that crosses page boundaries - which only applies for uncompressed instructions.

While this has limited immediate impact, as the instruction cache always stores instructions as u32 in the state - it makes more of an impact for the block cache - as instructions are stored as u16 or u32 directly. Splitting caching paths allows avoiding a check on the u32 to determine if it's 'actually' compressed or not.

Manually Testing

make -C src/riscv all

Benchmarking

	master	This MR	Improvement
$MyMachine	0.325 TPS (1/923 native)	0.339 TPS (1/885 native)	+4.3%
Benchmark Machine	0.150 TPS (1/1033 native)	0.151 TPS (1/1026 native)	+0.7%

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.

/assign @ole.kruger
/assign @victor-dumitrescu
/assign @felix.puscasu1
/assign @anastasia.courtney
/assign @emturner

/assign_reviewer @ole.kruger
/assign_reviewer @victor-dumitrescu
/assign_reviewer @felix.puscasu1
/assign_reviewer @anastasia.courtney
/assign_reviewer @emturner

/unassign me
/unassign_reviewer me

/ready