Narrow clippy expectations in tests

[SBALAVIGNESH123]

Summary

Follow-up to #71 CodeRabbit review.

This PR removes blanket file-level clippy expectations from engine tests and benchmark targets, then fixes the exposed lint debt directly where practical.

What changed

• Removed all #![expect(...)] file-level clippy expectations from crates/omnikv-engine/tests and crates/omnikv-engine/benches.
• Replaced broad suppressions with real cleanup for old format strings, doc-markdown findings, duplicate match arms, redundant clones, config initialization, unnecessary collects, and lock-scope tightening.
• Kept only narrow item/helper-level expectations where they are intentional:
  • benchmark throughput helper casts
  • benchmark soak harness length
  • two long Raft end-to-end scenario tests
• Preserved behavior while making future lint regressions visible to CI.

Why

CodeRabbit correctly pointed out that file-level #[expect] attributes can hide future lint debt in the same test target. This follow-up scopes the remaining exceptions to the smallest useful item and removes many exceptions entirely.

Validation

• cargo fmt --all -- --check
• git diff --check
• cargo clippy -p omnikv-engine --tests --benches -- -D warnings
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test -p omnikv-engine --test panic_policy_audit -- --test-threads=1
• cargo test -p omnikv-engine --test config_tests -- --test-threads=1
• cargo test -p omnikv-engine --test storage_correctness -- --test-threads=1
• cargo test -p omnikv-engine --test storage_tests -- --test-threads=1
• cargo test -p omnikv-engine --test durability_evidence -- --test-threads=1
• cargo test -p omnikv-engine --test operations -- --test-threads=1
• cargo test -p omnikv-engine --test benchmarks --release -- --test-threads=1 --nocapture
• rg -n "^#!\\[expect\\(" crates/omnikv-engine/tests crates/omnikv-engine/benches -g "*.rs" returned no matches.

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: be6e8193-6ec1-4b4b-a21c-b70f651de79c

📥 Commits

Reviewing files that changed from the base of the PR and between f4b1d63 and 44404e0.

📒 Files selected for processing (23)

• crates/omnikv-engine/benches/omni_bench.rs
• crates/omnikv-engine/benches/scan_buffer_pool.rs
• crates/omnikv-engine/benches/volcano_dispatch.rs
• crates/omnikv-engine/tests/anomaly_demos.rs
• crates/omnikv-engine/tests/api_error_sanitization_tests.rs
• crates/omnikv-engine/tests/benchmarks.rs
• crates/omnikv-engine/tests/concurrent_stress.rs
• crates/omnikv-engine/tests/config_tests.rs
• crates/omnikv-engine/tests/crash_consistency.rs
• crates/omnikv-engine/tests/debug_compaction.rs
• crates/omnikv-engine/tests/debug_compaction_200.rs
• crates/omnikv-engine/tests/debug_reopen.rs
• crates/omnikv-engine/tests/durability_evidence.rs
• crates/omnikv-engine/tests/operations.rs
• crates/omnikv-engine/tests/ops_maturity.rs
• crates/omnikv-engine/tests/panic_policy_audit.rs
• crates/omnikv-engine/tests/raft_cluster.rs
• crates/omnikv-engine/tests/sql_layer.rs
• crates/omnikv-engine/tests/sql_v3_features.rs
• crates/omnikv-engine/tests/storage_correctness.rs
• crates/omnikv-engine/tests/storage_engine.rs
• crates/omnikv-engine/tests/storage_perf.rs
• crates/omnikv-engine/tests/storage_tests.rs

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch agent/narrow-clippy-expect-scopes

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