[WIP] feat(15726): consolidate_blocks borrows from Python instead of cloning

[nomicflux]

Summary

Provides DecomposerRef to pass along PyRefs instead of cloning the underlying object. This provides a unified reference between Python refs & Rust refs, along with a streamlined apply function to encapsulate internals.

Details and comments

• AI tool used: OpenAI GPT-5.3-Codex for code analysis and technical advice. All code added was directly from me.
• Arguments to internal_consolidate_blocks packaged up into ConsolidateBlocksOptions to clean up the interface and make clearer that they are potential set in Python but also Nones from Rust.
• No new tests, as the behaviour should be identical to outside observers

Resolves #15726

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