Upgrade Rust toolchain 1.86 -> 1.89. Clean up compilation and linting warnings and errors.

Overview

Fix linting errors after Rust version upgrade.

NOTE: The diff will be updated and become much smaller once !220 (merged) is merged to master.

Install new Rust toolchain version

$ rustup toolchain install --profile default --component rustfmt,clippy 1.89

Changes

• Upgrade Rust toolchain: 1.86 -> 1.89
• Upgrade Debian image version in CI: bookworm -> trixie.
• Fix compilation warnings after Rust version upgrade.
• Fix linting errors after Rust version upgrade.

Related Merge Requests

• !220 (merged) (merge before current)
• !222 (merged) (merge after current)
• !223 (merged) (merge after current and after !222 (merged))