cmake: fix clang-tidy builds to verify tests, fix fallouts

- cmake: disable test bundles for clang-tidy builds.
  clang-tidy ignores #included .c sources, and incompatible with unity
  and bundles. It caused clang-tidy ignoring all test sources. It also
  means this is the first time tests sources are checked with
  clang-tidy. (autotools doesn't run it on tests.)

- cmake: update description for `CURL_TEST_BUNDLES` option.

- fix tests using special `CURLE_*` enums that were missing from
  `curl/curl.h`. Add them as reserved codes.

- fix about ~50 other issues detected by clang-tidy: unchecked results,
  NULL derefs, memory leaks, casts to enums, unused assigments,
  uninitialized `errno` uses, unchecked `open`, indent, and more.

- drop unnecessary casts (lib1533, lib3207).

- suppress a few impossible cases with detailed `NOLINT`s.

- lib/escape.c: drop `NOLINT` no longer necessary.
  Follow-up to 72abf7c13a #13862 (possibly)

- extend two existing `NOLINT` comments with details.

Follow-up to fabfa8e402 #15825

Closes #16756

tests/libtest/test.h

@@ -96,18 +96,18 @@ extern int unitfail;
 ** For portability reasons TEST_ERR_* values should be less than 127.
 */
 
-#define TEST_ERR_MAJOR_BAD     (CURLcode) 126
-#define TEST_ERR_RUNS_FOREVER  (CURLcode) 125
-#define TEST_ERR_EASY_INIT     (CURLcode) 124
-#define TEST_ERR_MULTI         (CURLcode) 123
-#define TEST_ERR_NUM_HANDLES   (CURLcode) 122
-#define TEST_ERR_SELECT        (CURLcode) 121
-#define TEST_ERR_SUCCESS       (CURLcode) 120
-#define TEST_ERR_FAILURE       (CURLcode) 119
-#define TEST_ERR_USAGE         (CURLcode) 118
-#define TEST_ERR_FOPEN         (CURLcode) 117
-#define TEST_ERR_FSTAT         (CURLcode) 116
-#define TEST_ERR_BAD_TIMEOUT   (CURLcode) 115
+#define TEST_ERR_MAJOR_BAD     CURLE_RESERVED126
+#define TEST_ERR_RUNS_FOREVER  CURLE_RESERVED125
+#define TEST_ERR_EASY_INIT     CURLE_RESERVED124
+#define TEST_ERR_MULTI         CURLE_RESERVED123
+#define TEST_ERR_NUM_HANDLES   CURLE_RESERVED122
+#define TEST_ERR_SELECT        CURLE_RESERVED121
+#define TEST_ERR_SUCCESS       CURLE_RESERVED120
+#define TEST_ERR_FAILURE       CURLE_RESERVED119
+#define TEST_ERR_USAGE         CURLE_RESERVED118
+#define TEST_ERR_FOPEN         CURLE_RESERVED117
+#define TEST_ERR_FSTAT         CURLE_RESERVED116
+#define TEST_ERR_BAD_TIMEOUT   CURLE_RESERVED115
 
 /*
 ** Macros for test source code readability/maintainability.
@@ -507,7 +507,7 @@ extern int unitfail;
   {                                             \
     (void)URL;                                  \
     fprintf(stderr, "Missing support\n");       \
-    return (CURLcode)1;                         \
+    return CURLE_UNSUPPORTED_PROTOCOL;          \
   }
 #endif
 
@@ -525,6 +525,6 @@ extern CURLcode test(char *URL); /* the actual test function provided by each
   {                                             \
     (void)URL;                                  \
     fprintf(stderr, "Missing support\n");       \
-    return (CURLcode)1;                         \
+    return CURLE_UNSUPPORTED_PROTOCOL;          \
   }
 #endif