fix: remove deprecated mp-units/format.h includes from audio examples

The audio examples were including the deprecated mp-units/format.h header
which generates deprecation warnings that are treated as errors with -Werror.
Removed the deprecated includes and ensured proper headers are included.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: rothmichaels

example/audio/0-wrapping_unsafe_apis.cpp

@@ -29,7 +29,8 @@ import std;
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
-#include <mp-units/format.h>
+#include <mp-units/math.h>
+#include <mp-units/systems/si.h>
 #endif
 
 #include "third_party_audio_api.h"

example/audio/1-oscillator.cpp

@@ -32,7 +32,6 @@ import std;
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
-#include <mp-units/format.h>
 #include <mp-units/math.h>
 #include <mp-units/systems/angular.h>
 #include <mp-units/systems/isq.h>