Skip computation of expression return dtype unless there are no chunks to return

[robert3005]

This would only ever catch implementation bugs and we explicitly handle empty
chunks case

[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
✅ 1235 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)]	161.9 µs	197.7 µs	-18.08%
⚡	Simulation	chunked_varbinview_opt_canonical_into[(1000, 10)]	224.8 µs	187.5 µs	+19.85%

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 rk/chunkedreader (fc2f879) with develop (06cf4a3)}