Move get_boundary functions without module dependencies to RzIO.

[Rot127]

Your checklist for this pull request

• [x] I've read the guidelines for contributing to this repository.
• [x] I made sure to follow the project's coding style.
• [x] I've documented every RZ_API function and struct this PR changes.
• [ ] I've added tests that prove my changes are effective (required for changes to RZ_API).
• [ ] I've updated the Rizin book with the relevant information (if needed).
• [ ] I've used AI tools to generate fully or partially these code changes and I'm sure the changes are not copyrighted by somebody else.

Detailed description

Moves some boundary functions because they are very useful and shouldn't depend on RzCore if everything they use is RzIO.

Test plan

All green, they are copied one to one.

Closing issues

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