Release 0.3.0: capture error-response body, Duration timeout, non_exhaustive errors

[azeemshaik025]

Summary

Breaking 0.3.0 — the trust-bar items from the review. Two breaking changes (constructor signature, error enum), one behind-the-scenes win.

Added

• The Http error variant now carries the response body. A non-2xx response keeps the raw payload the server returned — Http { status, reason, body } — so the reason a request was rejected is no longer discarded. Display appends the body when present. This is the floor for debugging against a real API.

Changed (breaking)

• Timeout is now a Duration. new / with_client take impl Into<Option<std::time::Duration>> instead of Option<u64> milliseconds. Pass Duration::from_secs(5) or None (5s default). Kills the footgun where Some(30) silently meant 30 milliseconds.
• The generated error enum is #[non_exhaustive] and Http gained a body field. Cross-crate exhaustive matches need a _ arm.

Migration

// before
let client = UserApi::new(url, Some(5000));
Err(UserApiError::Http { status, reason }) => { /* body was gone */ }

// after
let client = UserApi::new(url, Duration::from_secs(5));   // or None for the default
Err(UserApiError::Http { status, reason, body }) => { eprintln!("{status}: {body}"); }

Docs, examples & tests

• New error_handling.rs example — reading a failed request's body.
• Every example, the README (new Errors section), and the crate doctest moved to the Duration API and the error-body pattern.
• CHANGELOG [0.3.0] with the breaking-change notes and migration.

Verification

cargo fmt --check, cargo clippy --all-targets -- -D warnings, and 24 tests (incl. new test_http_error_captures_body) + doctests + all examples — all green. The 19 original behavior tests are unchanged (only the mechanical Some(5000) → Duration::from_secs(5) swap), so nothing existing regressed.

Not in this release

Typed error bodies (the err: DSL, #2 from the plan) — deferred; it builds on the raw-body capture landed here and wants its own design pass.