test(monero-rpc-pool): add database and status coverage

[copp1723]

Refs #801

Summary

• Add unit coverage for node address formatting, node record delegation, and health success-rate math.
• Add database tests for migrations, default node seeding, health-check aggregation, reliable node stats, and unknown-node handling.
• Add pool/app tests for current status reporting, status broadcasts, bandwidth sample gating, and initial app status publication.
• Add proxy tests for cloneable request/response buffering, JSON-RPC method/error extraction, clearnet whitelist behavior, and handler error JSON.
• Add tempfile as a dev dependency for isolated SQLite database directories.

Why

monero-rpc-pool had no library tests. These cover the core database, status, app startup, and proxy helper behavior without requiring live Monero nodes, Tor, or external services.

Verification

• RUSTUP_TOOLCHAIN=stable cargo fmt --check --manifest-path monero-rpc-pool/Cargo.toml
• git diff --check
• CARGO_HOME=/private/tmp/cargo-home RUSTUP_TOOLCHAIN=stable cargo test --manifest-path monero-rpc-pool/Cargo.toml --lib (15 passed)

[Einliterflasche]

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