feat(list): add allow and blocklist handling

This uses the .gitignore format to identify
which files should be allowed / blocked.

The allowlist gets precedence over the blocklist
if both are specified.

src/args.rs

@@ -18,6 +18,15 @@ pub struct Args {
     #[arg(long)]
     pub split_to: Option<PathBuf>,
 
+    /// An allowlist of files to keep, in .gitignore format.
+    /// Note: this will take precedence over all other removal decisions.
+    #[arg(long)]
+    pub allowlist: Option<PathBuf>,
+
+    /// A blocklist of files to remove, in .gitignore format.
+    #[arg(long)]
+    pub blocklist: Option<PathBuf>,
+
     /// The location of the sysroot to clean up
     pub sysroot_location: PathBuf,
 }