Fix startup failure due to timezonefinderL import error

The timezonefinderL package uses another package named importlib-resources. That package recently changed such that a method timezonefinderL uses (open_binary) is no longer available. That causes an import error, which in turn prevents composite from starting (assuming your configuration uses the device_or_utc or device_or_local choice for the time_as option.)

This change fixes that issue by changing the timezonefinder defaults. Specifically, the default package is now timezonefinder v6.2.0 instead of timezonefinderL v4.0.2, and the default class is now TimezoneFinderL instead of TimezoneFinder.

If, however, your configuration specifies the timezonefinderL package, you will need to manually change it to use the timezonefinder package instead. The easiest way to do that is to remove the tz_finder (and tz_finder_class) option(s) from your composite configuration.

See #49 for more details.