Add mypy for typechecking and vdr validation

[Scanteianu]

resolves #43

Summary of changes:

• mypy is now used to validate types
• the generated vdr is passed in through the python library's built in validator
• pick up locally cached NIST responses for much faster local development

I manually validated that the generated vdr is valid according to https://cyclonedx.github.io/cyclonedx-web-tool/

[karianna]

@Scanteianu Will need a rebase sorry!

[Scanteianu]

@steelhead31 @karianna Thanks both for the reviews! can I also get a merge please?