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/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};