feat(v2.2.2): prepare ExcelAlchemy 2.2.2

[ruicore]

Summary

This PR prepares the 2.2.2 release of ExcelAlchemy.

It continues the stable 2.x line with stronger developer ergonomics, clearer public API guidance, and better release-time smoke coverage, while keeping the public import/export workflow API stable.

What changed

Examples

• add examples/annotated_schema.py
• add examples/custom_storage.py
• add examples/fastapi_upload.py

These examples demonstrate:

• Annotated[..., Field(...), ExcelMeta(...)] declarations
• custom ExcelStorage integrations
• a realistic FastAPI upload workflow

Public API guidance

• add docs/public-api.md
• document:
  • stable public modules
  • compatibility modules
  • internal modules
  • recommended import style

Release hardening

• add scripts/smoke_package.py
• update the release workflow to run package-level smoke tests after wheel and source-distribution installation
• extend smoke coverage to template generation, import execution, and export artifact generation

Documentation updates

• update README.md
• update README_cn.md
• update MIGRATIONS.md
• add 2.2.2 changelog entry
• add docs/releases/2.2.2.md

Compatibility notes

• no public import/export workflow API was removed
• the new examples and docs clarify recommended public paths without changing existing 2.x compatibility behavior

Verification

• ./.venv/bin/ruff check .
• ./.venv/bin/uv run pyright
• ./.venv/bin/pytest -q
• ./.venv/bin/python scripts/smoke_package.py

Release intent

After merge, this branch is intended to be tagged and published as:

• v2.2.2

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.60%. Comparing base (38dbbf4) to head (7661dae).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #59      +/-   ##
==========================================
+ Coverage   86.56%   86.60%   +0.03%     
==========================================
  Files          48       48              
  Lines        3306     3306              
  Branches      375      375              
==========================================
+ Hits         2862     2863       +1     
+ Misses        277      276       -1     
  Partials      167      167              

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