ci: pin Clippy to Rust 1.98.1 and clear warnings

[lovasoa]

Summary

Pin the check job's Clippy toolchain to Rust 1.98.1, the current stable toolchain used by CI. This keeps Clippy from changing underneath the workflow when Rust stable advances.

Fix the six warnings Clippy 1.98.1 reports: redundant formatting references in the logger, PostgreSQL SASL, and query macros; truncate(0) instead of clear() for the MSSQL packet header; and a useless format! in a PostgreSQL type test.

Validation

• Core, root-package, and all-target Clippy commands pass for both Rustls and native-TLS on Rust 1.98.1.
• cargo fmt --all -- --check passes.