feat(refactor): refactor for easier usage

[zigzagcai]

Motivation

• support pip install: one-stop installation via python packaging
• easier API: from high-level 'TrainerBuilder', to mid-level ZeRO/FSDP/TP/PP/WP/SP/CP/EP parallelism, and low-level ops
• FSDP+EP: support FSDP working with Expert Parallelism, can be used for fast prototyping

Modification

Please briefly describe what modification is made in this PR.

BC-breaking (Optional)

None

Use cases (Optional)

None

Checklist

Before PR:

• Pre-commit or other linting tools are used to fix the potential lint issues.
• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests.
• The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, like docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects.
• CLA has been signed and all committers have signed the CLA in this PR.