refactor(common): add is_transient to Error enum

[raushan728]

Added an is_transient() method to the Error enum in google-apis-common to help users implement retry strategies. Distinguishes between permanent (e.g., 404) and transient (e.g., 503, 429, IO) errors. No external crates used.

[Byron]

Thanks a lot, this looks good to me once some small things have been addressed.
Thanks again.

Edit: And thanks for the disclosure. It's too bad commits are really easy to not see on GitHub.

[raushan728]

I took your suggestion to heart and enabled #![deny(missing_docs)] at the crate level for google-apis-common.
To satisfy the lint, I have documented all public items across lib.rs, auth.rs, serde.rs, and url.rs. This ensures that the crate remains fully documented and follows Rust best practices going forward

[raushan728]

@Byron plz take a look

[Byron]

Thanks a lot! I didn't realise how much still needed to be documented, and I am sorry for putting that on you.

With that said, I re-ran the documentation generation with Codex to get something much less generic.