[PR] feat: surface ObjectStoreOperation on outbound HTTP requests (HTTP backend) [arrow-rs-object-store]

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

adriangb opened a new pull request, #703:
URL: https://github.com/apache/arrow-rs-object-store/pull/703

   ## Summary
   
   Adds `ObjectStoreOperation { kind, location, backend }` carried via `http::Request::extensions` so a wrapping `HttpService` (tower layer, reqwest middleware, etc.) can produce useful trace spans without sniffing URLs and headers.
   
   `http::Extensions` is in-process only, so this is invisible on the wire — no behavior change for remote servers.
   
   ## Scope
   
   This PR instruments only the **HTTP** (WebDAV) backend: get / head / put / delete / copy / list (5 sites). The mechanism is in place and proven end-to-end, but AWS, GCP, and Azure each have their own request-construction style and are best landed as separate follow-up PRs (one per backend) to keep review surface small.
   
   ## Mechanism
   
   - `OperationKind` enum (`Get | Head | Put | PutMultipart | Delete | Copy | List | ListWithDelimiter`), `#[non_exhaustive]` for forward compatibility.
   - `ObjectStoreOperation::new(kind, backend).with_location(path)` — also `#[non_exhaustive]`.
   - `OperationKind::as_str()` returns a snake_case identifier suitable for span attributes (`object_store.operation = \"get\"` etc.).
   - `HttpRequestBuilder::operation(op)` helper that calls `request.extensions_mut().insert(op)` so it composes with the existing `extensions(http::Extensions)` setter without clobbering user-provided extensions.
   
   ## One subtle ordering constraint
   
   `GetOptionsExt::with_get_options` calls `self.extensions(extensions)` which **overwrites** the entire `http::Extensions` (existing behavior — not changed by this PR). So `.operation(...)` must be called *after* `.with_get_options(...)` on the get path. This is documented inline at the call site. A follow-up could make `extensions()` additive instead of overwriting if reviewers prefer that.
   
   ## Reading on the receiving side
   
   \`\`\`rust
   async fn call(&self, req: HttpRequest) -> Result<HttpResponse, HttpError> {
       if let Some(op) = req.extensions().get::<ObjectStoreOperation>() {
           span.set_attribute(\"object_store.operation\", op.kind.as_str());
           if let Some(loc) = &op.location {
               span.set_attribute(\"object_store.path\", loc.as_ref());
           }
           span.set_attribute(\"object_store.backend\", op.backend);
       }
       self.inner.call(req).await
   }
   \`\`\`
   
   ## Independence
   
   One of three independent additions for better HTTP integration seams. The others are \`impl HttpService for ClientWithMiddleware\` and \`TowerHttpConnector\`. Each PR is self-contained; they can be reviewed in any order. A tracking issue will follow once all three drafts are CI-green.
   
   ## Test plan
   
   - [x] 3 new unit tests in \`http::client::tests\` using a recording \`HttpService\` wrapper to assert kind/location/backend per operation (get, put, delete)
   - [x] \`cargo test --features=aws,azure,gcp,http --lib\` (190 tests pass)
   - [x] \`cargo fmt --all -- --check\`
   - [x] \`cargo clippy --features=aws,azure,gcp,http --lib --tests -- -D warnings\`
   - [ ] CI green
   - [ ] Follow-ups: instrument AWS, GCP, Azure backends in separate PRs
   
   🤖 Generated with [Claude Code](https://claude.com/claude-code)


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