Validate ignored doctests for CpuHnsw::build/with_capacity

[coderabbitai]

Summary

Ignored doctest examples in `CpuHnsw::build`/`CpuHnsw::with_capacity` bypass compile checking, and no trybuild/equivalent fixture covers the new API surface.

Required changes

Drop `rust,ignore` from the doctests or convert the examples into a validating doctest/trybuild fixture that exercises the public API and runs in CI.

Affected areas

• `chutoro-core/src/hnsw/cpu/construction.rs`

Acceptance criteria

• Doctest examples for `build`/`with_capacity` are compiled and checked in CI.

References

• PR: $pr_url
• Requested by: @$assignee

[coderabbitai]

🔗 Related PRs

leynos/repovec-appliance#4 - Design and roadmap.md [closed]
leynos/podbot#70 - 5.3.1 Stabilize Podbot public library boundaries for embedding [closed]
#122 - CPU session scaffold: SessionConfig, ClusteringSession, build_session [closed]
leynos/whitaker#221 - Document rstest companion test harness discovery and add unwrap exception tests [closed]
#130 - Refresh repository documentation guidance [merged]

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