Fix Clippy warnings (v0.12.x)

[tatsuya6502]

Fix the following Clippy warnings:

Stable: clippy 0.1.78 (9b00956e 2024-04-29)

• Allow clippy::incompatible_msrv on examples/reinsert_expired_entries_sync.rs, which requires Rust 1.70.0 or newer.

  warning: current MSRV (Minimum Supported Rust Version) is `1.65.0` but this item is stable since `1.70.0`
  --> examples/reinsert_expired_entries_sync.rs:50:9
     |
  50 |     SND.set(Mutex::new(snd.clone())).unwrap();
     |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Beta: clippy 0.1.79 (d9e85b56e7f 2024-05-25)

• Fix clippy::legacy_numeric_constants as suggested.
• Fix clippy::missing-transmute-annotations as suggested.
• Fix clippy::duplicated-attributes as suggested.

[tatsuya6502]

Merging.