Refactor butterfly server's dat_file field
Refactor butterfly server's dat_file field

- Change from RwLock to Mutex since there is no read/write distinction
- Don't incur the unlock cost to check if the option is some

Signed-off-by: Jon Bauman <e6c6a4db54ad11b4de69fed67139594b59f3444f@users.noreply.github.com>

habitat-sh/habitat,rsertelon/habitat,rsertelon/habitat,habitat-sh/habitat,rsertelon/habitat,habitat-sh/habitat,rsertelon/habitat,rsertelon/habitat,rsertelon/habitat,rsertelon/habitat,habitat-sh/habitat,habitat-sh/habitat,habitat-sh/habitat,habitat-sh/habitat,habitat-sh/habitat