Avoid re-building vortex-duckdb twice

[AdamGS]

Summary

Currently, if you build something like duckdb-bench cargo will rebuild vortex-duckdb once before it'll be satisfied that it doesn't need to rebuild it. The root cause is that cargo's fingerprinting can't accurately track files that are created during the build.

This change is fine because we still track our own changes, the only external change will be something like a duckdb version upgrade which will change build.rs and re-trigger the build as expected.

[codspeed-hq]

Merging this PR will degrade performance by 16.59%

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

❌ 1 regressed benchmark
✅ 1236 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	chunked_varbinview_opt_canonical_into[(1000, 10)]	187.7 µs	225.1 µs	-16.59%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing adamg/avoid-duckdb-rebuild (b5ba99c) with develop (2033ef5)}