DateTime can't be pickled when the container's timezone was set by copying /etc/localtime - #1040

Fixes #899.

My app runs in a Docker container where the timezone is set the common Alpine/Debian-slim way - cp /usr/share/zoneinfo/Asia/Kolkata /etc/localtime instead of symlinking it. That's a real, correctly-set timezone, but pendulum's get_local_timezone() doesn't recognize a copied file as named (it only reads a name from TZ, /etc/timezone, or a symlink target), so it falls back to reading the raw zoneinfo file directly via Timezone.from_file(). Any pendulum.now() I then try to pickle (I do this passing results back from a multiprocessing.Pool) crashes with _pickle.PicklingError: Cannot pickle a ZoneInfo file from a file stream, because zoneinfo.ZoneInfo.from_file() refuses to pickle anything built that way.

I know switching the Dockerfile to a symlink avoids this entirely, so arguably this is a deployment-config issue rather than a pendulum one. But Timezone.from_file() is already a deliberate, supported fallback here, not an error path - so I think it's worth making that fallback fully correct rather than leaving a trap nobody debugging a PicklingError would think to trace back to how /etc/localtime was set.

Kept the raw TZif bytes around on the instance when built via from_file(), and used them to rebuild an equivalent instance on unpickling instead of inheriting zoneinfo's version, which unconditionally rejects this. Regular Timezone(key) instances still pickle by key as before.