test: delete-policy unit and integration coverage

Unit: walker all-or-nothing bounds (exceeded -> nothing removed + distinct
result; exact bound -> deletes), protected-prefix skipping, config wire
round-trip for force_delete/delete_excluded/prune_empty_dirs/max_delete, CLI
parse/validation for the new flags.  Integration (TestDeletePolicy): default
delete-excluded protection and --delete-excluded opt-out (single-thread, -m,
early --delete-before, excluded-dir subtrees), --max-delete all-or-nothing over
and at the limit, --force file-over-nonempty-dir replacement, --prune-empty-dirs
(--dirs mode + recursion-mode parity), and --ignore-errors keeping deletion
active across a genuine scan I/O error (run as an unprivileged user).

tests/test_scanner.c

@@ -397,9 +397,8 @@ static void test_parallel_scanner_root_chunks_without_workers() {
   create_test_file(file1, "a");
   create_test_file(file2, "b");
 
-  ScannerOptions options = {false, 1,     NULL, 0,     NULL,  0,     0,
-                            0,     0,     0,    false, false, false, false,
-                            false, false, NULL, NULL,  false, false, false};
+  ScannerOptions options = {0};
+  options.chunk_size = 1;
   ParallelScanner* scanner = parallel_scanner_create_with_options(dir, &options, NULL);
   EXPECT_NOT_NULL(scanner);