feat(rust/rbac-registration): CIP509 validation refactoring

[stanislav-tkach]

Description

• Cip509::validate signature has been changed.
• Cip509Validation structure has been removed.

Description of Changes

The logic hasn't been changed, but now instead of returning an intermediate structure Result<Self> is returned.

Please confirm the following checks

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream module

[github-actions]

✅ Test Report | ${\color{lightgreen}Pass: 230/230}$ | ${\color{red}Fail: 0/230}$ |

[stanislav-tkach]

This probably makes the API less composable.