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

include/curl/curl.h

@@ -645,7 +645,20 @@ typedef enum {
   CURLE_UNRECOVERABLE_POLL,      /* 99 - poll/select returned fatal error */
   CURLE_TOO_LARGE,               /* 100 - a value/data met its maximum */
   CURLE_ECH_REQUIRED,            /* 101 - ECH tried but failed */
-  CURL_LAST /* never use! */
+  CURL_LAST, /* never use! */
+
+  CURLE_RESERVED115 = 115,       /* 115-126 - used in tests */
+  CURLE_RESERVED116 = 116,
+  CURLE_RESERVED117 = 117,
+  CURLE_RESERVED118 = 118,
+  CURLE_RESERVED119 = 119,
+  CURLE_RESERVED120 = 120,
+  CURLE_RESERVED121 = 121,
+  CURLE_RESERVED122 = 122,
+  CURLE_RESERVED123 = 123,
+  CURLE_RESERVED124 = 124,
+  CURLE_RESERVED125 = 125,
+  CURLE_RESERVED126 = 126
 } CURLcode;
 
 #ifndef CURL_NO_OLDIES /* define this to test if your app builds with all