Skip tokenizer/CST parsing when no CST rules are active

Check filter-rules-by-config before invoking the tokenizer in
lint-file. When all CST rules are disabled (e.g. --disable
comment-semicolons), the expensive tokenize+parse-cst pass is
skipped entirely.

On the Guix tree (1336 files), this saves ~2s on surface-only
runs (15.6s → 13.7s). The savings are more pronounced on
projects with fewer monster files.

gulie/engine.scm

@@ -93,17 +93,20 @@ and '%min-severity with value 'error, 'warning, or 'info (default)."
     (when (memq pass '(all surface))
       (set! diagnostics (append (run-line-rules file lines config)
                                 diagnostics))
-      ;; Pass 1b: CST rules (if tokenizer is loaded)
-      (let ((tok-mod (resolve-module '(gulie tokenizer) #:ensure #f)))
-        (when tok-mod
-          (let ((tokenize (module-ref tok-mod 'tokenize))
-                (cst-mod (resolve-module '(gulie cst) #:ensure #f)))
-            (when cst-mod
-              (let* ((parse-cst (module-ref cst-mod 'parse-cst))
-                     (tokens (tokenize text file))
-                     (cst (parse-cst tokens)))
-                (set! diagnostics (append (run-cst-rules file cst config)
-                                          diagnostics))))))))
+      ;; Pass 1b: CST rules — only tokenize if there are active CST rules
+      (let ((cst-rules (filter-rules-by-config (rules-of-type 'cst) config)))
+        (when (not (null? cst-rules))
+          (let ((tok-mod (resolve-module '(gulie tokenizer) #:ensure #f)))
+            (when tok-mod
+              (let ((tokenize (module-ref tok-mod 'tokenize))
+                    (cst-mod (resolve-module '(gulie cst) #:ensure #f)))
+                (when cst-mod
+                  (let* ((parse-cst (module-ref cst-mod 'parse-cst))
+                         (tokens (tokenize text file))
+                         (cst (parse-cst tokens)))
+                    (set! diagnostics
+                      (append (run-cst-rules file cst config)
+                              diagnostics))))))))))
     ;; Pass 2: semantic rules (if compiler module is loaded)
     (when (memq pass '(all semantic))
       (let ((comp-mod (resolve-module '(gulie compiler) #:ensure #f)))