Provide an easy-to-use top-level API to writing custom test packages

[kMutagene]

This is needed for people being able to author validation packages in https://github.com/nfdi4plants/arc-validate-packages.

Also related: #38

ideally, a validation package would look something like this:

#r "nuget: ARCValidation"
open ARCValidation

//<create a list of validation tests created via the API>
//eg:
let validationTests = [
    ValidationTest.create(<API logic here>)
    ValidationTest.create(<API logic here>)
]

//<end the script with an API function that applies the tests to an arc root path provided via cli args>
// This function would for example take a list of tests and apply it to tzhe first cli arg, which is checked to be a path
ARCValidation.runValidationTestsWithCLIArgs validationTests 

Note that a top-level API like this can also be used for the internal default tests that will always be performed by the tool, e.g. structural metadata file validation