fix(lint): add gen_corpus.ml and runtest rules to 5 fuzz directories

E718: Add gen_corpus.ml to ocaml-crypto, ocaml-csrf, ocaml-git,
ocaml-github-oauth, ocaml-gpt
E724: Add (rule (alias runtest) ...) for property-based testing

bench/pack_bench.ml

···
         in
         ()
       done;
-      Printf.printf "Done: folded %d objects x 100 iterations\n%!"
+      Fmt.pr "Done: folded %d objects x 100 iterations\n%!"
         (Git.Pack.count pack)

fuzz/dune

···
  (modules fuzz fuzz_common fuzz_index fuzz_config)
  (libraries git crowbar))
 
-; Quick check with Crowbar (no AFL instrumentation)
+(executable
+ (name gen_corpus)
+ (modules gen_corpus)
+ (libraries unix))
+
 (rule
- (alias fuzz)
+ (alias runtest)
  (deps fuzz.exe)
- (action (run %{exe:fuzz.exe})))
+ (action
+  (run %{exe:fuzz.exe})))
 
-; AFL-instrumented build target
 (rule
- (alias fuzz-afl)
+ (alias fuzz)
  (deps fuzz.exe)
- (action (echo "AFL fuzzer built: %{exe:fuzz.exe}\n")))
+ (action
+  (echo "AFL fuzzer built: %{exe:fuzz.exe}\n")))

fuzz/gen_corpus.ml

···
+(** Generate seed corpus for fuzz testing. *)
+
+let () =
+  (try Unix.mkdir "corpus" 0o755
+   with Unix.Unix_error (Unix.EEXIST, _, _) -> ());
+  let write name data =
+    let oc = open_out_bin (Filename.concat "corpus" name) in
+    output_string oc data;
+    close_out oc
+  in
+  write "seed_000" "";
+  write "seed_001" "\x00\x00\x00\x00";
+  write "seed_002" "DIRC\x00\x00\x00\x02";
+  write "seed_003" "[core]\n\tbare = false\n";
+  write "seed_004" "blob 5\x00hello";
+  write "seed_005" (String.make 20 '\xab');
+  write "seed_006" "tree 0\x00"

test/test_common.mli

···
 (** Shared test utilities. *)
 
 val hash : Git.Hash.t Alcotest.testable
-
-val with_temp_repo :
-  (Eio.Fs.dir_ty Eio.Path.t -> Fpath.t -> 'a) -> 'a
+val with_temp_repo : (Eio.Fs.dir_ty Eio.Path.t -> Fpath.t -> 'a) -> 'a
 
 val commit :
   repo:Git.Repository.t ->

test/test_pack.ml

···
       let oc = open_out file in
       (* Write 10KB of content - enough to trigger delta compression *)
       for i = 1 to 500 do
-        Printf.fprintf oc "Line %d: This is some repetitive content.\n" i
+        Fmt.pf oc "Line %d: This is some repetitive content.\n" i
       done;
       close_out oc;
       ignore (run_git tmp_dir [ "add"; "large.txt" ]);
···
       (* Modify just a few lines - this will create a delta *)
       let oc = open_out file in
       for i = 1 to 500 do
-        if i = 250 then Printf.fprintf oc "Line %d: MODIFIED CONTENT HERE!\n" i
-        else Printf.fprintf oc "Line %d: This is some repetitive content.\n" i
+        if i = 250 then Fmt.pf oc "Line %d: MODIFIED CONTENT HERE!\n" i
+        else Fmt.pf oc "Line %d: This is some repetitive content.\n" i
       done;
       close_out oc;
       ignore (run_git tmp_dir [ "add"; "large.txt" ]);

test/test_pack_index.ml

···
               "valid kind" true
               (match kind with `Commit | `Tree | `Blob | `Tag -> true)
         | Error (`Msg m) ->
-            Alcotest.fail
-              (Printf.sprintf "object %d at offset %d: %s" i offset m)
+            Alcotest.fail (Fmt.str "object %d at offset %d: %s" i offset m)
       done
   | Error (`Msg m), _ -> Alcotest.fail ("pack: " ^ m)
   | _, Error (`Msg m) -> Alcotest.fail ("index: " ^ m)