fix(nuget): tighten bounded CPM props resolution

[mstykow]

Summary

• bound NuGet Directory.Packages.props / Directory.Build.props import following to the actual active scan root and deny out-of-scope .props reads
• preserve imported ordinary .props central package versions during assembly while keeping partially unresolved composed expressions unresolved
• record the resulting real-world end state in docs/BENCHMARKS.md with refreshed standalone dotnet/extensions and new microsoft/regorus compare-output snapshots

Issues

• Covers: bounded NuGet CPM import and composition follow-up from PR fix(parsers): expand static dependency indirection coverage #826 plus the blocker fixes uncovered during post-implementation review
• Closes:

Scope and exclusions

• Included:
  • parser scan-root plumbing in src/parsers/mod.rs, src/scanner/collect.rs, and src/scanner/process/orchestrator.rs
  • NuGet .props import/path handling and composed property resolution in src/parsers/nuget/ and src/assembly/nuget_cpm_resolve.rs
  • focused parser and assembly regression coverage for out-of-root import denial, partial-resolution fail-closed behavior, and imported-version preservation
  • benchmark/docs updates for:
    • microsoft/regorus @ 7f42115 from .provenant/compare-runs/20260430T114610Z-regorus-348
    • dotnet/extensions @ 7171956 refresh from .provenant/compare-runs/20260430T115315Z-extensions-9749
• Explicit exclusions:
  • no full MSBuild evaluation
  • no conditioned PropertyGroup or ItemGroup evaluation beyond the existing bounded behavior
  • no support for Directory.Build.targets, wildcard imports, or arbitrary non-literal import graphs
  • no scorecard edit, since the NuGet verification row is already marked verified

Intentional differences from Python

• Provenant continues to prefer bounded static resolution over broad evaluator behavior.
• It now resolves composed central PackageVersion expressions and bounded repository-local .props imports only when the imported file stays under the active scan root.
• It intentionally fails closed on partially unresolved composed expressions instead of collapsing them into misleading concrete-looking versions.

Follow-up work

• Created or intentionally deferred:
  • deferred: broader conditioned MSBuild semantics for project/package versions outside the current bounded slice
  • deferred: any future support for non-CPM import graphs or Directory.Build.targets

Expected-output fixture changes

• Files changed:
  • no golden fixture files were regenerated; coverage was added in unit tests and compare-output evidence instead
• Why the new expected output is correct:
  • the parser now denies .props imports that escape the active scan root, so out-of-scope property bags are no longer read or surfaced
  • imported ordinary .props package versions are preserved during assembly even when local raw PackageVersion entries also exist
  • final standalone compare-output runs confirm the user-visible end state:
    • microsoft/regorus resolves Microsoft.Regorus to 0.9.1 in central props and consumer dependencies
    • dotnet/extensions root and nested Directory.Packages.props surfaces now carry imported central package-version dependency metadata instead of empty imported-props placeholders