Read SPDX 3 by spdx-python-model

[bact]

• Implement a thin layer for SPDX 3 (any 3.x version) support
• Using spdx-python-model as binding for SPDX 3 data model
• Use function names and structure that follow existing public SPDX 2 API of tools-python

This PR is trying to be small, focusing on ground work (format detection, etc), and demonstrate one core functionality (reading a file).

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A SpdxObjectSet Protocol structural type is introduced for convenience of type checking.
It will allow functions to have a type that is not specific to a SPDX 3.x minor version (spdx_python_.model.v3_0_1.SHACLObjectSet and spdx_python_.model.v3_1.SHACLObjectSet are considered different types).

The plan forward is to use the spdx_tools.spdx3.SpdxObjectSet (and spdx_tools.spdx3.SpdxObject, etc) protocol that derived directly from SPDX 3 RDF+SHACL (generated via spdx-python-model) as SPDX 3 data models' representation -- and remove the entire src/spdx_tools/spdx3/model to avoid maintenance of the multiple model versions (SPDX 3.0, SPDX 3.1, etc).

[bact]

Note: Alternatively, we can implement the SpdxObjectSetProtocol in spdx-python-model instead. (see full proposal at spdx/spdx-python-model#45; and PRs at JPEWdev/shacl2code#114 and spdx/spdx-python-model#52)

This will allow anyone, including the more complete SPDX 3 implementation like ones in PR #898, to use the abstraction and freed them from managing model versions.