Use DUCKDB_SOURCE_DIR if supplied

[myrrc]

If duckdb-vortex is supplied, don't attempt to download duckdb

[codspeed-hq]

Merging this PR will not alter performance

⚠️ 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 improved benchmark
❌ 1 regressed benchmark
✅ 1530 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	chunked_varbinview_canonical_into[(1000, 10)]	161.8 µs	198.1 µs	-18.31%
⚡	Simulation	chunked_varbinview_canonical_into[(100, 100)]	308.5 µs	273.5 µs	+12.8%

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 myrrc/duckdb-src-env (bdbe62f) with develop (eda4dd0)}