chore(deps): update rust crate bon to v3.9.3

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
bon	dependencies	patch	3.9.1 → 3.9.3

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[doubleword-code]

Summary

This PR (correctly titled as updating to v3.9.3 despite the title saying v3.9.2) updates the bon crate from version 3.9.1 to 3.9.3. This is a routine patch-level dependency update with only bugfixes—no API changes or breaking changes.

Verdict: Ready to approve. The changes are safe and purely beneficial.

Research notes

I reviewed the official changelog for versions 3.9.2 and 3.9.3:

• v3.9.3 (2026-06-15): Fixed clippy::missing_docs_in_private_items triggering for start_fn members (#389)
• v3.9.2 (2026-06-10): Fixed rust-analyzer "Go to Definition" inside #[builder] functions (#385), plus regular maintenance

Both releases contain only internal/developer-experience improvements with zero changes to the Rust API surface.

Suggested next steps

1. Consider updating the PR title from "v3.9.2" to "v3.9.3" for accuracy (the actual update in Cargo.lock is to 3.9.3).
2. Merge as-is—no code changes required in the consuming codebase.

General findings

The bon crate is used in this repository via #[derive(Builder)] on structs in src/target.rs (e.g., ProviderSpec, PoolSpec, TargetSpec, Target) and src/errors.rs (OnwardsErrorResponse). The usage patterns—including #[builder(default)] and #[builder(default = default_weight())]—are unaffected by these patch releases.

No security concerns, no breaking changes, and no regressions expected.