Topiary panics with -vv when the configuration is not a regular file

[Xophmeister]

When Topiary's logging attempts to output the name of the configuration file -- with -vv (or higher) -- and the configuration file is not a regular file, then it panics. Here:

topiary/topiary-config/src/source.rs

Lines 126 to 130 in f35eee4

	Self::File(path) => {
	// We only stringify the path when we know it exists, so the call to `canonicalize`
	// is safe to unwrap. (All bets are off, if called from elsewhere.)
	write!(f, "{}", path.canonicalize().unwrap().to_string_lossy())
	}

By "not a regular file" I mean, for example, via process substitution:

$ topiary config -vvC <(cat topiary-config/languages.ncl)
[2025-01-03T16:52:08Z INFO  topiary_config::source] Could not find configuration file: /home/chris/.config/topiary. Defaulting to built-in configuration.
thread 'main' panicked at topiary-config/src/source.rs:129:53:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Using process substitution like this is a good way to create a quick-and-dirty self-contained wrapper script. While this is not something that should be encouraged, Topiary shouldn't crash in this case (or, at least, the error message should be more instructive).