fix: make logging safer

[0xwitty]

spotted a few things that could crash the app:

• switched record.args().as_str().unwrap() → &format!("{}", record.args()) so logs work even if arguments aren’t strings.
• tweaked Formatter → Formatter<'_> for the right type in the format function.
• replaced unwrap() on RUST_LOG with if let Ok(val) = env::var("RUST_LOG") to avoid panicking when it’s not set.

now logging should be smoother and safer :)