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

CMakeLists.txt

@@ -300,9 +300,14 @@ if(ENABLE_CURLDEBUG)
   list(APPEND CURL_DEBUG_MACROS "CURLDEBUG")
 endif()
 
+option(CURL_TEST_BUNDLES "Build tests into single-binary bundles" OFF)
+
 option(CURL_CLANG_TIDY "Run the build through clang-tidy" OFF)
 if(CURL_CLANG_TIDY)
+  # clang-tidy is not looking into #included sources, thus not compatible with
+  # unity builds and test bundles.
   set(CMAKE_UNITY_BUILD OFF)
+  set(CURL_TEST_BUNDLES OFF)
   set(_tidy_checks "")
   list(APPEND _tidy_checks "-clang-analyzer-security.insecureAPI.strcpy")
   list(APPEND _tidy_checks "-clang-analyzer-optin.performance.Padding")