[snippy] Dump initial registers without model

[MaxGud10]

Fixes #12

Previously, initial register state was dumped only through the simulator path.

As a result, --dump-initial-registers-yaml did not work when model-plugin was
set to None, even though the initial register state was already available.

This change dumps the initial register state directly in the no-model path.

Added a regression test based on the reproducer from the issue.

[arromanoff]

In general it now looks like snippy will dump initial registers with and without model via different mechanisms (in simulator and this new dump... function). Can we unify them instead?

[arromanoff]

Suggested change

	# RUN: llvm-snippy %s -mtriple=riscv64-unknown-elf -num-instrs=10 \
	# RUN: llvm-snippy %s -mtriple=riscv64 -num-instrs=10 \

[arromanoff]

Also add -model-plugin None

[arromanoff]

Please, don't

[arromanoff]

Can we reuse sections from Inputs/ directory?

[MaxGud10]

Updated the PR on top of the current main and addressed the review comments.

Initial register dumping is now handled through SnippyProgramContext and reused from both model and no-model paths. The test was also updated to use Inputs/sections.yaml, remove the manual cleanup step, and explicitly pass --model-plugin=None.

[arromanoff]

I don't like this new member and it's usage
We dump register state after we generated code so there're no problems with getting subtarget from LLVMState at this point. Just call getLLVMState().getSubtargetImpl

[arromanoff]

There on the call site you can get the subtarget

auto *EntryFunc  = MainModule.getFunction(ProgramCfg.EntryPointName);
assert(EntryFunc);
auto &ST = State.getSubtargetImpl(*EntryFunc);
// Now you can call
dumpInitialRegisterState(PassCfg.RegistersConfig.InitialStateOutputYaml, ST);

[arromanoff]

Hence this overload is redundant

[arromanoff]

I'd also separate concerns here. Let's separate fetching this state and dumping it. So in FlowGenerator you can do:

auto &RegState = ProgramCtx.getInitialRegisterState(ST);
RegState.saveAsYAMLFile(PassCfg.RegistersConfig.InitialStateOutputYaml);