chore(rust/signed-doc): Refactor catalyst-signed-doc tests, move most of the rules unit tests into the separate tests.rs files

[Mr-Leshiy]

Description

Refactoring PR, moving most of the rules unit tests into their own tests.rs files.
This approach of separation a huge amount of test code, would increase the readability of the actual code

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 | ${\color{lightgreen}Pass: 520/520}$ | ${\color{red}Fail: 0/520}$ |

[apskhem]

LGTM