feat: Rename pockettts service to vox and improve numba caching

Renamed the systemd service from "pockettts" to "vox" for better branding and clarity.
Updated the  script to reflect the new service name.

Addressed numba caching issues when running as a systemd service:
- Created  to explicitly set  to a project-local directory ().
- Modified  to import  early in the execution flow.
- Updated the systemd service file to grant write permissions to the  directory.
- Added  to  to prevent caching files from being committed.

voices/preferences.json

@@ -1,5 +1,5 @@
 {
   "user_voices": {
-    "122139828182712322": "hankhill"
+    "122139828182712322": "gibralter_good"
   }
 }