fix: preserve instance context in generated helpers

[AGiorgetti]

Change

Fixes #22.

• Track selected instance dependencies independently of declared-mapping and cycle metadata, then propagate them through the generated helper graph.
• Emit instance nested/collection helpers only when needed; keep instance-free siblings static and preserve equivalent helper sharing.
• Exclude instance-only mappings/defaults from static entry resolution.
• Add 20 executable regressions, stateful Basic/clean-package consumer coverage, and synchronized usage/changelog/control documentation.

Verification

• Test-first: the initial 16 cases produced 14 failures and two controls before production edits. The completed 20-case matrix on unchanged develop produced 18 failures and two controls, zero skips. The normal Basic sample independently reproduced CS0120.
• Final local generator suite: 634 passed, zero failed/skipped, including all 20 new cases. Runtime 5/5 and integration 1/1 pass. Release solution build has zero warnings/errors; all three source sample smoke runs pass.
• Available packaging suite: 220 passed, two infrastructure failures, zero skips. This includes all 12 framework/language combinations, clean package-backed samples, package/API checks, usage validation, and benchmark smoke. The enhanced clean Basic consumer rebuilt/reran with no warnings; emitted instance-helper source was inspected.
• Trimming and Native AOT are locally blocked at ILLink ComputeManagedAssemblies task-host creation (MSB4216 / Unix-domain SocketException 13). PowerShell and clang are absent; 49 PowerShell-dependent cases were not run locally. No local trimming/AOT success is claimed.
• An earlier parallel package attempt had 196 passes and 26 infrastructure failures; DOTNET_PROCESSOR_COUNT=1 recovered ordinary packaging/consumer validation without altering source, assertions, or dependencies.
• Independent read-only review found no correctness blocker. CRLF-aware diff validation and consumer-skill validation pass.
• Remote tree fc6094d3494b0e6bf9e71c9eec8f8a2df784ba65 matches the tested/staged local tree. Exact-head ordinary CI run 37789425394 passed for beffec6. Linux and Windows each passed 911 tests with zero failures/skips, including trimming and Native AOT. All six Roslyn 4.8/4.14/5.9 jobs passed 634 tests each with zero failures/skips. Linux sample smoke checks and all five benchmark smoke cases passed.
• Pack & Validate, Verify Release Artifacts, and Publish NuGet Packages were skipped in this ordinary PR run.

Opened as draft for human review. The maintainer merged this PR on 2026-10-08 at 14:12:53 UTC as d80ff4c. No agent merge, release, tag push, package publication, or workflow dispatch was performed. Other issues remain outside this fix.

Prepared with OpenAI Codex.