[cicm4]

Open4D now uses .o4d for compressed sequence files, inspect_o4d / pack_o4d / unpack_o4d for public helpers, and O4D for labels and newly authored USD prims. Existing encoded bytes retain their signatures, schema and native payload layout; a standalone file can be renamed without conversion, and compressed USD files using the former prim remain readable.

This PR includes the complete branch change set:

• Add standalone native carriage, codec discovery, legacy migration and compressed USD round trips for the twelve public codecs.
• Add ORBIT loading, RGB-D capture/reconstruction, QUEEN/3DGStream preparation, Gaussian serialization, browser delivery and decoded-mesh TCP transport.
• Prepare the lightweight open4d wheel/source distribution with explicit package boundaries, optional extras, an installed CLI, strict metadata checks, clean-install CI and trusted-publishing gates. Research runtimes remain external; the Open3D adapter installs under open4d.integrations.
• Fix partial 3DGStream decoder configuration and preserve single-component TSMC coefficient matrices.
• Include the existing removal of large checked-in datasets, generated reconstructions, papers/media and the Unity example archive; update the existing documentation and examples.

Validation:

• All 32 GitHub checks passed on d7fa75e, including the Python 3.10–3.13 optional-feature installation/rendering matrix and the aggregate CI passed gate.
• macOS core suite: 920 passed, 150 skipped. Linux with optional dependencies and native regression fixtures: 1,141 passed, 21 skipped.
• Installed browser streamer on Linux: 614 passed, 1 skipped, including JavaScript parsing and HTTP transfer checks.
• Clean wheel and source installations on Python 3.10, 3.11, 3.12 and 3.13; installed I/O, CLI, codec discovery, O4D round trips and TCP streaming passed. All optional-feature smoke checks passed in the GPU runtime, including actual four-frame GIF rendering under software OpenGL.
• Installed-wheel encode/fresh-decode/repeated-decode cycles passed for all eight mesh codecs on a two-frame C3 dataset subset. The TSMC single-component GPU regression and byte-identical O4D/USD round trip passed.
• Fresh-process CUDA decoding of QUEEN, 3DGStream, Vega and ReRF from renamed files and compressed USD passed. Pre-rename fixtures and all four native representations preserve identical payload bytes through unpack/repack and legacy/current USD.
• Wheel/source builds, strict Twine checks, exact source inventory, documentation links, provenance checks and staged whitespace checks passed. The complete branch diff retains pre-existing whitespace in native patch files and an extra EOF blank line in open4d/_streamer.py.

Publication remains blocked by the repository's 19 unresolved provenance entries and recorded maintainer-approval requirement. Native research backends require their separately configured runtimes; the format is custom Open4D carriage and does not claim MPEG interoperability. Live camera hardware was not exercised.

The PR commits are authored and committed by cicm (camilocorreall44@gmail.com), associated with cicm4, without additional contributor trailers.