[ktz03]

Fixes #1559

Changes

• Forward the documented transport_params["compression"] option to smart_open.open as its top-level compression keyword. This fixes forced decompression of extensionless gzip/bzip2 files and preserves raw bytes when decompression is disabled.
• Copy the transport mapping before extracting the option, preserving caller options and other transport parameters. Add real-file regressions for text/binary reads, disabled decompression, default extension inference and checkpoint restoration; correct the existing mock assertion.

Validation

• The complete FileReader module passes all 29 tests, including offline Moto S3 emulation. On the unchanged production code, the six affected real-file cases fail while the two inference controls pass.
• All seven pinned full-repository pre-commit hooks and the documentation completeness check pass.
• Mypy 1.8.0 reports no type errors in 35 source files. The existing quoted Python-version setting emits a configuration warning; an additional run explicitly targeting Python 3.13 also succeeds.
• The complete test/nodes/ suite passes: 405 passed, 15 existing CUDA skips. Tested locally on Windows/Python 3.12.14 with Torch 2.14.0+cpu and smart_open 8.0.4; no live cloud-service test was run.