chore: fix clippy lints for rust 1.97

[prabhaks]

What

Rust/clippy 1.97 (now on CI's stable toolchain) introduced new lints that fail the clippy check (cargo hack clippy --each-feature --no-dev-deps -- -D warnings) against existing code on main. This currently breaks the coverage job on every open PR, not just one. This PR fixes those lints so CI goes green again.

Lints fixed

• for_kv_map: iterate map.values() instead of map.iter() when the key is unused (rbac/mod.rs, sse/mod.rs, alerts/target.rs, connectors/kafka/metrics.rs)
• useless_borrows_in_formatting: drop the redundant & in format! arguments (storage/s3.rs, storage/gcs.rs, metastore/.../object_store_metastore.rs, handlers/airplane.rs, handlers/http/alerts.rs, handlers/http/cluster/mod.rs, metrics/prom_utils.rs, query/listing_table_builder.rs)
• cloned_ref_to_slice_refs: use std::slice::from_ref(x) instead of &[x.to_string()] (users/filters.rs)
• collapse a match on a Result into the ? operator (parseable/streams.rs)

These are mechanical, behavior-preserving fixes, mostly produced by cargo clippy --fix. No functional change.

Verification

Ran locally with clippy 1.97.0 (matching CI):

• cargo clippy --no-deps -- -D warnings: clean
• cargo clippy --no-default-features --no-deps -- -D warnings: clean

The kafka feature fix (connectors/kafka/metrics.rs) is the same for_kv_map pattern applied elsewhere; its native librdkafka build was not run locally, so CI's --each-feature kafka run will validate it.

Summary by CodeRabbit

• Refactor
  • Simplified internal iteration and formatting logic across alert, metrics, storage, authentication, and request-handling workflows.
  • Streamlined schema error propagation during disk-file conversion.
  • Preserved existing alert deletion, broker metrics, authorization, broadcasting, URL generation, and request behavior.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 6f447d48-265e-48cb-ad9d-1654837e385c

📥 Commits

Reviewing files that changed from the base of the PR and between 47cff47 and a003dd2.

📒 Files selected for processing (14)

• src/alerts/target.rs
• src/connectors/kafka/metrics.rs
• src/handlers/airplane.rs
• src/handlers/http/alerts.rs
• src/handlers/http/cluster/mod.rs
• src/metastore/metastores/object_store_metastore.rs
• src/metrics/prom_utils.rs
• src/parseable/streams.rs
• src/query/listing_table_builder.rs
• src/rbac/mod.rs
• src/sse/mod.rs
• src/storage/gcs.rs
• src/storage/s3.rs
• src/users/filters.rs

---

Walkthrough

The PR removes unnecessary borrows, unused map keys, and verbose error propagation across Rust modules. Existing iteration behavior, path construction, authorization, error handling, and storage URL generation remain unchanged.

Changes

Rust cleanup

Layer / File(s)	Summary
Collection iteration cleanup src/alerts/target.rs, src/connectors/kafka/metrics.rs, src/rbac/mod.rs, src/sse/mod.rs	Alert, broker, user, and session loops now iterate directly over values instead of unused key/value pairs.
Formatting and path construction cleanup src/handlers/..., src/metastore/..., src/metrics/prom_utils.rs, src/query/listing_table_builder.rs, src/storage/...	Unnecessary references are removed from formatted SQL, URIs, object-store paths, metrics URLs, and storage URLs.
Error and authorization argument cleanup src/parseable/streams.rs, src/users/filters.rs	Schema errors use ? propagation, and dataset authorization receives a borrowed one-item slice.

Estimated code review effort: 2 (Simple) | ~10 minutes

Poem

I nipped each needless borrow away,
And let value-only loops lead the day.
Paths still point, metrics still sing,
Errors still fly on the question-mark wing.
Hop, hop—clean Rust takes spring!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: fixing Clippy lint failures for Rust 1.97.
Description check	✅ Passed	The description covers the goal, lint categories fixed, rationale, and verification, matching the template well.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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