Fix capacity-overflow panic in print_snip at --terminal-width 1

`InteractivePrinter::print_snip` computes the snip separator width as
`term_width - panel_count - snip_left_count - title_count`. At `--terminal-width 1`
the panel is disabled and `title_count == 2`, so the subtraction underflows
`usize` (release has no overflow-checks, so it wraps to ~usize::MAX); `str::repeat`
then aborts with "capacity overflow" whenever a snip separator is emitted (two or
more disjoint line ranges, or a diff gap) — which the default style does.

Use `saturating_sub` for the repeat counts so they clamp to 0 instead of
underflowing. Added an integration test.

tests/integration_tests.rs

@@ -305,6 +305,19 @@ fn line_range_multiple() {
         .stdout("line 1\nline 2\nline 4\n");
 }
 
+#[test]
+fn snip_at_terminal_width_one_does_not_panic() {
+    bat()
+        .arg("multiline.txt")
+        .arg("--style=snip")
+        .arg("--color=always")
+        .arg("--terminal-width=1")
+        .arg("--line-range=1:2")
+        .arg("--line-range=4:4")
+        .assert()
+        .success();
+}
+
 #[test]
 fn line_range_multiple_with_context() {
     bat()