feat: Add MLflow as a first-class offline DataSource for Feast

[Vperiodt]

What this PR does / why we need it:

Adds MlflowDatasetSource so Feast can read tabular MLflow data for offline retrieval via get_historical_features() and create_saved_dataset().

• Dual-mode source: GenAI Dataset (dataset_name/dataset_id) and artifact (run_id + artifact_path, Parquet/CSV)
• Offline support: DuckDB/ibis direct read, plus to_arrow() fallback for other stores
• Auth: Bearer token propagation from Feast requests to MLflow (request context → env → ServiceAccount)
• CLI: sync-dataset, preview-dataset, validate-source, list-sources
• Graceful degradation when mlflow is not installed; non-MLflow FeatureViews unaffected

Which issue(s) this PR fixes:

Checks

• I've made sure the tests are passing.
• My commits are signed off (git commit -s)
• My PR title follows conventional commits format

Testing Strategy

• Unit tests
• Integration tests
• Manual tests
• Testing is not required for this change

Misc

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 35.17787% with 492 lines in your changes missing coverage. Please review.
✅ Project coverage is 46.70%. Comparing base (037c4cd) to head (3932595).

Files with missing lines	Patch %	Lines
sdk/python/feast/cli/mlflow_cmd.py	0.00%	179 Missing ⚠️
...dk/python/feast/mlflow_integration/dataset_sync.py	41.17%	139 Missing and 31 partials ⚠️
...infra/data_sources/mlflow/mlflow_dataset_source.py	55.40%	59 Missing and 7 partials ⚠️
sdk/python/feast/infra/offline_stores/duckdb.py	6.12%	46 Missing ⚠️
sdk/python/feast/infra/data_sources/mlflow/auth.py	67.79%	15 Missing and 4 partials ⚠️
sdk/python/feast/infra/offline_stores/ibis.py	11.11%	8 Missing ⚠️
sdk/python/feast/permissions/security_manager.py	66.66%	2 Missing ⚠️
sdk/python/feast/permissions/server/arrow.py	0.00%	1 Missing ⚠️
sdk/python/feast/permissions/server/rest.py	0.00%	1 Missing ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6702      +/-   ##
==========================================
- Coverage   46.76%   46.70%   -0.06%     
==========================================
  Files         415      420       +5     
  Lines       50392    51150     +758     
  Branches     7214     7346     +132     
==========================================
+ Hits        23567    23891     +324     
- Misses      25171    25564     +393     
- Partials     1654     1695      +41     

Flag	Coverage Δ
go-feature-server	30.58% <ø> (ø)
python-unit	48.00% <35.17%> (-0.09%)	⬇️

Files with missing lines	Coverage Δ
...python/feast/infra/data_sources/mlflow/__init__.py	100.00% <100.00%> (ø)
sdk/python/feast/mlflow_integration/config.py	91.48% <100.00%> (+91.48%)	⬆️
sdk/python/feast/permissions/server/arrow.py	52.38% <0.00%> (-1.28%)	⬇️
sdk/python/feast/permissions/server/rest.py	35.29% <0.00%> (-1.07%)	⬇️
sdk/python/feast/permissions/security_manager.py	89.77% <66.66%> (-1.70%)	⬇️
sdk/python/feast/infra/offline_stores/ibis.py	38.99% <11.11%> (-1.21%)	⬇️
sdk/python/feast/infra/data_sources/mlflow/auth.py	67.79% <67.79%> (ø)
sdk/python/feast/infra/offline_stores/duckdb.py	34.65% <6.12%> (-4.62%)	⬇️
...infra/data_sources/mlflow/mlflow_dataset_source.py	55.40% <55.40%> (ø)
...dk/python/feast/mlflow_integration/dataset_sync.py	41.17% <41.17%> (ø)
... and 1 more

... and 4 files with indirect coverage changes

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