chore: update `wallet.rs` in-line BIP doc

[K1-R1]

This PR makes a small addition to the in-line docs of new_from_mnemonic_phrase_with_path to clarify that it is not restricted to BIP32 derivation paths only.

Checklist

• [x] I have linked to any relevant issues.
• [x] I have updated the documentation.
• [x] I have added tests that prove my fix is effective or that my feature works.
• [x] I have added necessary labels.
• [x] I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• [x] I have requested a review from the relevant team or maintainers.

Closes #1369