tests: make individual test sources compile cleanly

Tidy up headers and includes to ensure all individual test source
compile cleanly (but not link). To allow running clang-tidy (and
possibly other static analyzers) on them. It also improves readability
and allows to verify them locally, without the bundle logic.

clang-tidy ignores #included C files, so it's blind to bundle C files
the include these tests. The current workaround of embedding has
a couple of downsides:. meaningless filenames and line numbers,
missing issues, messing up self header paths. Thus, running it on
individual sources would be beneficial.

Also:
- de-duplicate includes.
- untangle some includes.
- formatting/indentation fixes.
- merge `getpart.h` into `first.h`.

Ref: https://github.com/curl/curl/pull/17680#issuecomment-2991730158

Closes #17703

tests/client/first.c

@@ -21,6 +21,7 @@
  * SPDX-License-Identifier: curl
  *
  ***************************************************************************/
+#include "first.h"
 
 int main(int argc, char **argv)
 {
@@ -35,7 +36,7 @@ int main(int argc, char **argv)
 
   entry_name = argv[1];
   entry_func = NULL;
-  for(tmp = 0; tmp < CURL_ARRAYSIZE(s_entries); ++tmp) {
+  for(tmp = 0; s_entries[tmp].ptr; ++tmp) {
     if(strcmp(entry_name, s_entries[tmp].name) == 0) {
       entry_func = s_entries[tmp].ptr;
       break;

tests/client/first.h

@@ -32,6 +32,8 @@ struct entry_s {
   entry_func_t ptr;
 };
 
+extern const struct entry_s s_entries[];
+
 #include <curl/curl.h>
 
 #include "curlx.h"

tests/client/h2_pausing.c

@@ -23,6 +23,8 @@
  ***************************************************************************/
 /* This is based on the PoC client of issue #11982
  */
+#include "first.h"
+
 #include <assert.h>
 
 static void usage_h2_pausing(const char *msg)

tests/client/h2_serverpush.c

@@ -21,6 +21,7 @@
  * SPDX-License-Identifier: curl
  *
  ***************************************************************************/
+#include "first.h"
 
 static int my_trace(CURL *handle, curl_infotype type,
                     char *data, size_t size, void *userp)

tests/client/h2_upgrade_extreme.c

@@ -21,6 +21,7 @@
  * SPDX-License-Identifier: curl
  *
  ***************************************************************************/
+#include "first.h"
 
 static size_t write_h2ue_cb(char *ptr, size_t size, size_t nmemb, void *opaque)
 {

tests/client/hx_download.c

@@ -21,6 +21,7 @@
  * SPDX-License-Identifier: curl
  *
  ***************************************************************************/
+#include "first.h"
 
 static int verbose_d = 1;
 

tests/client/hx_upload.c

@@ -21,6 +21,7 @@
  * SPDX-License-Identifier: curl
  *
  ***************************************************************************/
+#include "first.h"
 
 static int verbose_u = 1;
 

tests/client/tls_session_reuse.c

@@ -21,6 +21,7 @@
  * SPDX-License-Identifier: curl
  *
  ***************************************************************************/
+#include "first.h"
 
 static size_t write_tse_cb(char *ptr, size_t size, size_t nmemb, void *opaque)
 {

tests/client/upload_pausing.c

@@ -23,6 +23,8 @@
  ***************************************************************************/
 /* This is based on the PoC client of issue #11769
  */
+#include "first.h"
+
 static size_t total_read = 0;
 
 static size_t read_callback(char *ptr, size_t size, size_t nmemb,

tests/client/ws_data.c

@@ -21,6 +21,8 @@
  * SPDX-License-Identifier: curl
  *
  ***************************************************************************/
+#include "first.h"
+
 #ifndef CURL_DISABLE_WEBSOCKETS
 
 static CURLcode check_recv(const struct curl_ws_frame *frame,

tests/client/ws_pingpong.c

@@ -21,6 +21,8 @@
  * SPDX-License-Identifier: curl
  *
  ***************************************************************************/
+#include "first.h"
+
 #ifndef CURL_DISABLE_WEBSOCKETS
 
 static CURLcode ping(CURL *curl, const char *send_payload)