Fix generation of stat pruning expression for unsupported dtypes

[robert3005]

Flagged by the fuzzer and likely doesn't happen in practice but better to be
defensive here in case we add complex partials

this is alternative version of #8302

[codspeed-hq]

Merging this PR will improve performance by 20.24%

⚠️ 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.

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 6 improved benchmarks
✅ 1520 untouched benchmarks

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	chunked_bool_canonical_into[(1000, 10)]	46.7 µs	31.9 µs	+46.56%
⚡	Simulation	chunked_varbinview_canonical_into[(1000, 10)]	197.9 µs	161.8 µs	+22.3%
⚡	Simulation	chunked_varbinview_into_canonical[(1000, 10)]	213.6 µs	177.1 µs	+20.61%
⚡	Simulation	encode_varbin[(1000, 8)]	162.2 µs	144.6 µs	+12.16%
⚡	Simulation	encode_varbin[(1000, 4)]	161.4 µs	144.2 µs	+11.94%
⚡	Simulation	encode_varbin[(1000, 32)]	167.1 µs	150.1 µs	+11.32%

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing rk/statfixes (0c6b621) with develop (4b6c382)}