fix(src/metadata.rs): remove unused std::fs::File import (#25)

Unused import promoted to compile error by `RUSTFLAGS=-Dwarnings` on
test + coverage jobs, blocking every Dependabot PR. `rg` confirms `File`
is referenced nowhere else in the file.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: hyperpolymath

src/metadata.rs

@@ -16,7 +16,6 @@
 
 use crate::ImagePair;
 use anyhow::Result;
-use std::fs::File;
 use std::io::{BufWriter, Write};
 use std::path::Path;