ENH: set NDEBUG for release builds

NDEBUG is normally expected to be set for release builds, however
for historical reasons Meson does not (yet) toggle `NDEBUG` for
non-debug builds (which we already default to). So set this as the
default. Choosing 'if-release' so that if users are explicitly
asking for a debug build via config-settings, they don't see a change
in behavior.

xref numpy/numpy#22546 (comment)

mesonpy/__init__.py

@@ -851,6 +851,7 @@ def _configure(self, reconfigure: bool = False) -> None:
             f'--native-file={os.fspath(self._meson_native_file)}',
             # TODO: Allow configuring these arguments
             '-Ddebug=false',
+            '-Db_ndebug=if-release',
             '-Doptimization=2',
 
             # XXX: This should not be needed, but Meson is using the wrong paths