Move to importlib.util.find_spec for checking if packages are installed

[nhairs]

Per title, move to importlib.util.find_spec over try: import name; catch ImportError.

This allows us to check for installed modules (i.e. orjson, msgspec) without actually importing them.

Ref: https://stackoverflow.com/a/14050282/12281814

[nhairs]

Fixed in #27