fix(docs): Update and remove signed document metadata from docs

[saibatizoku]

Description

Updates information regarding using UUIDv7 instead of ULID in docs/comments.
Moves docs/src/architecture/08_concepts/signed_document_metadata to catalyst-libs.

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 | ${\color{lightgreen}Pass: 334/334}$ | ${\color{red}Fail: 0/334}$ |

[github-actions]

✅ Test Report | ${\color{lightgreen}Pass: 334/334}$ | ${\color{red}Fail: 0/334}$ |