[PR] feat: impl HttpService for reqwest_middleware::ClientWithMiddleware [arrow-rs-object-store]

["adriangb (via GitHub)" <gi...@apache.org>]

adriangb opened a new pull request, #702:
URL: https://github.com/apache/arrow-rs-object-store/pull/702

   ## Summary
   
   Mirrors the existing `impl HttpService for reqwest::Client` so consumers who already build a middleware stack on `reqwest_middleware::ClientBuilder` can hand the resulting `ClientWithMiddleware` straight to `HttpClient::new` without writing adapter boilerplate.
   
   The most common use case this unblocks is W3C trace-context propagation via `reqwest_tracing::TracingMiddleware`, but any `reqwest_middleware::Middleware` (retry, caching, conditional, request-id, etc.) composes the same way.
   
   ## Design
   
   - Gated behind a new opt-in `reqwest-middleware` feature (off by default; implies `cloud`).
   - Pinned to `reqwest-middleware = "0.4"` because object_store's `reqwest = "0.12"` is incompatible with `reqwest-middleware = "0.5"` which requires `reqwest 0.13`. Bump together when object_store moves to reqwest 0.13.
   - The impl is non-wasm only: `reqwest-middleware`'s `Middleware` trait requires `Send + Sync` while the wasm `HttpService` plumbing uses `?Send`, and there's no clean way to reuse the channel-based wasm body logic for this convenience layer.
   - `HttpError::reqwest_middleware` is added next to the existing `HttpError::reqwest`. `Reqwest(_)` variants delegate to the existing classification; opaque `Middleware(_)` variants fall back to `HttpErrorKind::Unknown` (downstream middleware authors can construct richer kinds via `HttpError::new` if they want).
   
   ## Usage
   
   \`\`\`rust
   use object_store::client::HttpClient;
   use reqwest_middleware::ClientBuilder;
   use reqwest_tracing::TracingMiddleware;
   
   let inner = reqwest::Client::new();
   let client = ClientBuilder::new(inner)
       .with(TracingMiddleware::default())
       .build();
   let http = HttpClient::new(client);
   \`\`\`
   
   …or hand it via `HttpBuilder::with_http_connector` for the high-level builders.
   
   ## Independence
   
   This PR is one of three independent additions for better HTTP integration seams. The others are:
   
   - `ObjectStoreOperation` extension on outbound requests (per-call operation context for tracing wrappers).
   - `TowerHttpConnector` (general `tower::Service` adapter).
   
   Each PR is self-contained and behind its own feature; they can be reviewed in any order. A tracking issue will follow once all three drafts are CI-green.
   
   ## Test plan
   
   - [x] New unit test \`client_with_middleware_runs_middleware\` mirroring \`spawn.rs\`'s mock-server pattern, confirming middleware mutates the request the server sees
   - [x] \`cargo test --features=aws,azure,gcp,http,reqwest-middleware --lib\` (188 tests pass)
   - [x] \`cargo check --no-default-features --features reqwest-middleware\` (feature isolation)
   - [x] \`cargo fmt --all -- --check\`
   - [x] \`cargo clippy --all-features --lib --tests -- -D warnings\`
   - [ ] CI green (this draft is opened to validate CI)
   
   🤖 Generated with [Claude Code](https://claude.com/claude-code)


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