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

lib/strerror.c

@@ -335,6 +335,20 @@ curl_easy_strerror(CURLcode error)
   case CURLE_OBSOLETE62:
   case CURLE_OBSOLETE75:
   case CURLE_OBSOLETE76:
+
+    /* error codes used by curl tests */
+  case CURLE_RESERVED115:
+  case CURLE_RESERVED116:
+  case CURLE_RESERVED117:
+  case CURLE_RESERVED118:
+  case CURLE_RESERVED119:
+  case CURLE_RESERVED120:
+  case CURLE_RESERVED121:
+  case CURLE_RESERVED122:
+  case CURLE_RESERVED123:
+  case CURLE_RESERVED124:
+  case CURLE_RESERVED125:
+  case CURLE_RESERVED126:
   case CURL_LAST:
     break;
   }