Indent every scope and put opening braces on the signature line

Namespace and extern "C" bodies are indented a level, so nesting is
visible from the indentation rather than only from the braces. Opening
braces stay on the line that opens the scope, including function
definitions, which previously carried theirs on a line of their own.

tests/fixtures/src/bad_version.cpp

@@ -20,19 +20,16 @@
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <https://www.gnu.org/licenses/>.
  */
-extern "C" const char* dpm_module_version(void)
-{
+extern "C" const char* dpm_module_version(void) {
     return "banana";
 }
 
-extern "C" const char* dpm_module_description(void)
-{
+extern "C" const char* dpm_module_description(void) {
     return "Fixture with a malformed version.";
 }
 
 extern "C" int dpm_module_execute(void* ctx, const char* command,
-                                  int argc, char** argv)
-{
+                                  int argc, char** argv) {
     (void)ctx;
     (void)command;
     (void)argc;

tests/fixtures/src/good.cpp

@@ -24,21 +24,18 @@
  */
 #include <cstring>
 
-extern "C" const char* dpm_module_version(void)
-{
+extern "C" const char* dpm_module_version(void) {
     return "1.2.3";
 }
 
-extern "C" const char* dpm_module_description(void)
-{
+extern "C" const char* dpm_module_description(void) {
     return "Known-good stub module.";
 }
 
 /* Answers "ping" with 42 so a dispatch round trip is observable, and
    0 for anything else. */
 extern "C" int dpm_module_execute(void* ctx, const char* command,
-                                  int argc, char** argv)
-{
+                                  int argc, char** argv) {
     (void)ctx;
     (void)argc;
     (void)argv;

tests/fixtures/src/missing_symbols.cpp

@@ -21,12 +21,10 @@
  * along with this program. If not, see <https://www.gnu.org/licenses/>.
  */
 
-extern "C" const char* dpm_module_version(void)
-{
+extern "C" const char* dpm_module_version(void) {
     return "1.0.0";
 }
 
-extern "C" const char* dpm_module_description(void)
-{
+extern "C" const char* dpm_module_description(void) {
     return "Fixture missing most of the contract.";
 }

tests/test_core.cpp

@@ -50,14 +50,12 @@ static int g_checks   = 0;
         }                                                                  \
     } while (0)
 
-static bool error_contains(dpm_ctx* ctx, const char* needle)
-{
+static bool error_contains(dpm_ctx* ctx, const char* needle) {
     const char* err = dpm_last_error(ctx);
     return err != nullptr && std::strstr(err, needle) != nullptr;
 }
 
-int main(void)
-{
+int main(void) {
     /* ---- dpm_open: invalid explicit override refuses ---- */
     {
         dpm_open_overrides bad = {"/does/not/exist/conf", nullptr, nullptr, -1};