Syntax: Implement Restricted AT URI Syntax Validation in Rust

[afbase]

Background

As discussed in GitHub Issue #39, the current implementation of AT URI validation conforms mostly to the general syntax, but not the more restricted syntax specified in the AT URI Scheme Specification. A stricter validation function that adheres to the Restricted AT URI Syntax would be useful.

Done When

1. Create ensure_valid_restrict_at_uri function: Implement a new validation function that enforces the following requirements of the Restricted AT URI Syntax.
2. Add tests for the new validation function: Create test cases to ensure the updated function correctly validates Restricted AT URIs.
3. Document the changes: Update the ATURI_VALIDATION.md file to reflect the new validation behavior.

Related References

• Typescript Reference implementation of the syntax package
• AT URI Scheme Specification
• GitHub Issue #39