feat(outbox): support getting outbox messages by level in node pvm

[zcabter]

Part of RV-874

What

Exposes get_outbox_messages in the NodePvm

Why

This is required to enable the Rollup Node to query outbox messages for a specific level, which reflects the RPC endpoint that it will ultimately expose.

How

Exposes get_outbox_messages for use exclusively in Normal mode. It should never be invoked in code paths that require proof as it could potentially blow up proof size

Manually Testing

make all

Regressions

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.
• Explain changes to regression test captures when applicable.
• Write commit messages in agreement with our guidelines.
• Self-review your changes to ensure they are high-quality.
• Complete all of the above before assigning this MR to reviewers.

[codecov]

Codecov Report

❌ Patch coverage is 97.16981% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.19%. Comparing base (301d866) to head (ca06d23).

Files with missing lines	Patch %	Lines
src/riscv/lib/src/pvm/node_pvm.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           vdum/rv-877     #815      +/-   ##
===============================================
+ Coverage        91.16%   91.19%   +0.02%     
===============================================
  Files              110      110              
  Lines            21206    21312     +106     
  Branches         21206    21312     +106     
===============================================
+ Hits             19333    19436     +103     
- Misses            1498     1501       +3     
  Partials           375      375              

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