Fix structure formatting to include link indexes

[konard]

Summary

• Merged the latest main into issue-19-9de6817b and resolved the stale root-level C# conflict.
• Fixed --structure formatting so expanded structure output keeps link indexes and renders zero/non-expanded references explicitly.
• Kept structure expansion on the left/source branch while rendering the right/target side as a reference, matching the expected shape like (4: (3: (2: (1: 0 0) 1) 1) 2).
• Applied the same behavior to the C# CLI and Rust implementation.

Fixes #19

Reproduction Covered

The previous C# formatter produced output like:

(4:(3:(2:(1: ) 1) 1) 2)

Rust expanded both sides and omitted link indexes. New tests cover the expected indexed output, including the 0 0 leaf case and repeated source/target references.

Tests

• dotnet restore, dotnet build --no-restore --configuration Release, dotnet test --no-build --configuration Release --verbosity normal from csharp/
• cargo fmt --all -- --check, RUSTFLAGS=-Dwarnings cargo clippy --all-targets --all-features, cargo test --all-features --verbose, cargo test --doc --verbose from rust/
• npm run test:wasm
• npm run build

[konard]

Previous solution is wrong. We also need to get latest changes from default branch and resolve conflicts.

What I expect to see in that case is like:

(4: (3: (2: (1: 0 0) 1) 1) 2)

And that should be covered extensively with tests in both C# and Rust implementation.

[konard]

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Starting automated work session at 2026-05-08T06:08:00.057Z

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[konard]

Working session summary

Implemented and finalized PR 48: #48

Resolved the main merge conflict, replaced the incorrect structure formatting, and added C# plus Rust coverage. --structure now preserves link indexes and explicit references, e.g. (4: (3: (2: (1: 0 0) 1) 1) 2).

Verification completed:

• C# restore/build/test passed
• Rust fmt/clippy/test/doc-test passed
• npm run test:wasm passed
• npm run build passed
• Fresh GitHub CI for head 00d4b6c passed for C#, Rust, and WebAssembly
• PR is marked ready for review and merge status is CLEAN
• Local worktree is clean

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[konard]

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[konard]

✅ Ready to merge

This pull request is now ready to be merged:

• All CI checks have passed
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• No pending changes

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