Add configurability and native SPDX validator, modernize packaging (#3)

This turned into a ground-up rewrite which includes the following:
* Add configurability of completeness checker requirements
* Add native SPDX 2.3 validator that is fully spec compliant
* Modernize Python packaging configuration (pyproject.toml, uv.lock)

Signed-off-by: Jesse Porter <jporter@qti.qualcomm.com>

Add initial CLI application and library functionality (#2)

Co-authored-by: Porter, Jesse <quic_jporter@quicinc.com>

Signed-off-by: McGuire, Kevin <quic_kmcguire@quicinc.com>
Signed-off-by: Porter, Jesse <quic_jporter@quicinc.com>