Allow switching back to SAPI speech client via a "plugin tweak"

src/calibre/gui2/tts/implementation.py

@@ -4,6 +4,10 @@
 from calibre.constants import iswindows, ismacos
 
 if iswindows:
+    from calibre.utils.config_base import tweaks
+    if tweaks.get('prefer_winsapi'):
+        from .windows_sapi import Client
+    else:
         from .windows import Client
 elif ismacos:
     from .macos import Client