Apply clang-format

* use clang-format v17.0.6 to reformat the tree
* tweak some places so that clang-format does not mutate the layout
  of code too much

Signed-off-by: Kefu Chai <tchaikov@gmail.com>

src/fmt.cc

@@ -101,7 +101,7 @@ extern "C++" {
 
 // gcc doesn't yet implement private module fragments
 #if !FMT_GCC_VERSION
-module : private;
+module :private;
 #endif
 
 #include "format.cc"