keep file catalogers separate from file-related definitions

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

internal/archive/test-fixtures/generate-zip-fixture-from-source-dir.sh

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+set -eux
+
+# $1 —— absolute path to destination file, should end with .zip, ideally
+# $2 —— absolute path to directory from which to add entries to the archive
+
+pushd "$2" && find . -print | zip "$1" -@ && popd

internal/archive/test-fixtures/zip-source/b-file.txt

@@ -0,0 +1 @@
+B file...

internal/archive/test-fixtures/zip-source/some-dir/a-file.txt

@@ -0,0 +1 @@
+A file! nice!