refactor: inline single-use parse_bucket_name

[alukach]

What

parse_bucket_name was a one-line split_once wrapper called from a single place (get_bucket). Inline it.

let (account, product) = name
    .split_once(crate::BUCKET_SEPARATOR)
    .ok_or_else(|| ProxyError::BucketNotFound(name.to_string()))?;

Why

A named helper that wraps a single stdlib call and has one caller is indirection without payoff. The call site is just as clear with split_once inline.

Verification

Full pre-push suite (fmt, clippy wasm32, wasm check, tests) green.

Found via ponytail over-engineering audit.

🤖 Generated with Claude Code

[claude]

Claude finished @alukach's task in 32s —— View job

---

✅ No blocking issues — safe to merge.

The inlining is mechanically correct — behavior is identical to the removed helper. One minor observation:

• src/registry.rs:53: The comment hardcodes "account:product" rather than referencing crate::BUCKET_SEPARATOR. If the constant ever changes, the comment will silently lie. Not blocking, but replacing the literal with BUCKET_SEPARATOR's actual value from the constant (or just removing the format hint and leaving only the pre-mapped note) would be more durable.

[github-actions]

🚀 Latest commit deployed to https://source-data-proxy-pr-158.source-coop.workers.dev

• Date: 2026-06-18T23:36:44Z
• Commit: 1919dbc