adds support for modern xray patching

[TimSimpsonR]

This adds two new functions to xray which does things the new modern
way, using aws_xray_sdk.

To use it from a typical lambda module, do this:

from fleece import xray

...

xray.patch(["main_project_package"])

def lambda_handler(event: dict, context: t.Any) -> None:
    log = global_log.new(**xray.log_args(context))
    log.info(event)
    ...