fix: graceful error on non-UTF-8 --time-style value instead of panic

[SAY-5]

Description

eza --time-style VALUE aborted with a panic (exit 134) when VALUE was not valid UTF-8, e.g. eza --time-style "$(printf '\xff\xfe')" .. The custom TimeFormatParser::parse_ref called value.to_str().unwrap(), and OsStr::to_str() returns None for non-UTF-8, so the .unwrap() panicked.

This makes the parser return a clap InvalidUtf8 usage error when the value is not valid UTF-8, matching how every other flag rejects bad input. The sibling env-var path in view.rs already handles this with to_str().unwrap_or("").

Fixes #1837.

How Has This Been Tested?

cargo test --lib passes, including a new #[cfg(unix)] regression test that feeds a non-UTF-8 --time-style value and asserts a usage error rather than a panic. Manually confirmed eza --time-style "$(printf '\xff\xfe')" . now prints error: invalid UTF-8 in --time-style value instead of crashing. cargo fmt and cargo clippy --lib are clean.