v0.8.0

add zenroom script validation (#14)

* started adding script class
* added from_json and to_json, added test cases for output validation
* updated changelog and version bump
* optional script passed through tx generate functions
* added script test cases, added optional script to transaction
* added script validation to tx constructor
* updated cc dependency, removed remnants of zenroom signing
* updated poetry.lock
* added zenroom dependency

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Signed-off-by: Lorenz Herzberger <lorenzherzberger@gmail.com>