Add identity chain actions, switch from hex to base58, switch to borsh for signature, refactor identity chain

[zupzup]

📝 Description

Future PRs in this task: adding atomicity for surrealdb blockchain actions and rollback logic in case of errors

This PR refactors the identity chain to use in-module data objects and a fail-safe API to add blocks.
It also switches from hex to base58 encoding and to borsh for the signature.
It also re-implements changing identity fields to use an Option-based approach.

Relates to #140

---

✅ Checklist

Please ensure the following tasks are completed before requesting a review:

• My code adheres to the coding guidelines of this project.
• I have run cargo fmt.
• I have added or updated tests (if applicable).
• All CI/CD steps were successful.
• I have updated the documentation (if applicable).
• I have checked that there are no console errors or warnings.
• I have verified that the application builds without errors.
• I've described the changes made to the API. (modification, addition, deletion).

---

🚀 Changes Made

• New Features:

  • Added actions for identity chain

• Refactoring:

  • Identity chain API

• Other Changes:

  • Changed hex to base58

---

💡 How to Test

Please provide clear instructions on how reviewers can test your changes:

• Run tests
• Create a company, add/remove signatories, Create a new identity and do signed bill actions and make sure the according Identity Chain entries are added to surrealdb

---

🤝 Related Issues

List any related issues, pull requests, or discussions:

• Identity chain #140

---

📋 Review Guidelines

Please focus on the following while reviewing:

• Does the code follow the repository's contribution guidelines?
• Are there any potential bugs or performance issues?
• Are there any typos or grammatical errors in the code or comments?

[codecov]

Codecov Report

Attention: Patch coverage is 96.54939% with 51 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/web/handlers/identity.rs	0.00%	16 Missing ⚠️
src/service/company_service.rs	97.53%	14 Missing ⚠️
src/web/handlers/company/mod.rs	0.00%	6 Missing ⚠️
src/util/mod.rs	77.77%	4 Missing ⚠️
src/blockchain/mod.rs	88.00%	3 Missing ⚠️
src/service/identity_service.rs	96.93%	3 Missing ⚠️
src/blockchain/bill/chain.rs	85.71%	2 Missing ⚠️
src/service/mod.rs	0.00%	2 Missing ⚠️
src/blockchain/identity/mod.rs	99.62%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!