chore(types): add return type hint to gen_sha512_hash

[q33566]

Description

Added a missing return type hint (-> str) to the gen_sha512_hash function to improve type safety and readability.

• [x] I have tested these changes locally.
• [x] I have reviewed the code changes.
• [ ] I have updated the documentation (if necessary).
• [ ] I have added appropriate unit tests (if applicable).