Sync DeepMatch with recent DeepCTR CI and TensorFlow compatibility updates

[shenweichen]

Summary

Sync DeepMatch with the latest compatibility/CI direction from recent DeepCTR master updates.

• Merge CI into a single workflow with one matrix job covering TF1/TF2 targets
• Add docs-only fast path via dorny/paths-filter and workflow concurrency controls
• Migrate private tensorflow.python.keras imports to public tensorflow.keras APIs across code, examples, tests, and docs
• Add/update TensorFlow compatibility guidance in README/Quick-Start/FAQ/index
• Add ReadTheDocs v2 config and refresh docs build requirements
• Update package/version metadata (0.3.2) and release notes entry

Validation

• python -m compileall deepmatch tests examples passed locally
• Unit tests were not run locally because TensorFlow is not installed in the current local environment

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.62%. Comparing base (93ca437) to head (e86d8c4).
⚠️ Report is 1 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (93ca437) and HEAD (e86d8c4). Click for more details.

HEAD has 10 uploads less than BASE

Flag	BASE (93ca437)	HEAD (e86d8c4)
pytest	14	4

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #107       +/-   ##
===========================================
- Coverage   89.88%   72.62%   -17.26%     
===========================================
  Files          12       15        +3     
  Lines         939     1001       +62     
===========================================
- Hits          844      727      -117     
- Misses         95      274      +179     

Flag	Coverage Δ
pytest	72.62% <100.00%> (-17.26%)	⬇️

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