[QDP] File and streaming Quantum Data Loader

[rich7420]

Purpose of PR

Adds file-backed and streaming Parquet data sources to the Quantum Data Loader. Users can call .source_file(path) or .source_file(path, streaming=True) and iterate in batches. PyO3 loader bindings are restored so QuantumDataLoader works with synthetic, file, and streaming sources.

• qdp-core: DataSource::InMemory and DataSource::Streaming; new_from_file (full read, supports .parquet/.arrow/.npy/.pt/.pb etc.) and new_from_file_streaming (Parquet, chunked read). Shared path_extension_lower, take_batch_from_source, named constants, first-chunk buffer reuse. Basis encoding fix: state vector allocated as Float64 to match kernel, then converted to engine precision.
• qdp-python (Rust): PyQuantumLoader, create_synthetic_loader, create_file_loader, create_streaming_file_loader (Linux only). batch_limit=None → usize::MAX; path from str or Path; file/streaming build in py.detach().
• loader.py: source_file(path, streaming=False), _create_iterator(). Streaming requires .parquet.
• Tests: New loader tests (mutual exclusion, batch count, extension, streaming). DLPack and bindings tests updated for current error messages.

Related Issues or PRs

Related to #969

Changes Made

• Bug fix
• New feature
• Refactoring
• Documentation
• Test
• CI/CD pipeline
• Other

Breaking Changes

• Yes
• No

Checklist

• Added or updated unit tests for all changes
• Added or updated documentation for all changes
• Successfully built and ran all unit tests or manual tests locally
• PR title follows "MAHOUT-XXX: Brief Description" format (if related to an issue)
• Code follows ASF guidelines

[400Ping]

Please resolve conflicts

[guan404ming]

Overall looks nice, left one question

[guan404ming]

I think both _source_type string and three boolean flags track the same information. Maybe we could consider to keep only booleans since this would eliminate ~10 lines of validation logic in _create_iterator().

[rich7420]

nice catch!

[guan404ming]

Overall looks nice! Please help resolve conflict and I think we are good to merge~

[400Ping]

@rich7420 Please solve conflicts

[400Ping]

Overall LGTM

[guan404ming]

Thanks for the update!

[rich7420]

thanks for the review!
@guan404ming , @400Ping