RISC-V: run all jstz-bench messages in a single level

• Closes RV-212
• Relates to RV-211

What

Run all messages for the jstz-bench scenario in a single level.

Why

Will allow to run the scenario in WASM without reboots (so that we get the like-for-like GC slowdown).

NB this requires a small additional piece of kernel work, that we don't reboot jstz for each message individually. This will be a follow up MR.

How

The logic of this is entirely contained in the inbox-bench binary. Since we loose the upfront information of how many transfers were expected (second level of inbox file), we now pass through the expected number in from the script.

Manually Testing

make -C src/riscv all

Benchmarking

While no changes to the kernel/sandbox are made, we now no longer include the StartOfLevel, InfoPerLevel or EndOfLevel messages in the duration.

	master	This MR	Improvement
AMD Ryzen 7 7840U	0.329 TPS (1/857 native)	0.346 TPS (1/907 native)	+5.2% (-5.8%)
Benchmark Machine	0.151 TPS (1/1033 native)	0.155 TPS (1/1016 native)	+2.6% (+1.6%)

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