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/unit/unit1620.c

@@ -58,11 +58,14 @@ static void test_parse(
   fail_unless(!!exp_options == !!options, "options expectation failed");
 
   if(!unitfail) {
-    fail_unless(!exp_username || strcmp(userstr, exp_username) == 0,
+    fail_unless(!userstr || !exp_username ||
+                strcmp(userstr, exp_username) == 0,
                 "userstr should be equal to exp_username");
-    fail_unless(!exp_password || strcmp(passwdstr, exp_password) == 0,
+    fail_unless(!passwdstr || !exp_password ||
+                strcmp(passwdstr, exp_password) == 0,
                 "passwdstr should be equal to exp_password");
-    fail_unless(!exp_options || strcmp(options, exp_options) == 0,
+    fail_unless(!options || !exp_options ||
+                strcmp(options, exp_options) == 0,
                 "options should be equal to exp_options");
   }