fix[array]: get_item reduce + struct wrong nullability

[joseph-isaacs]

fixes: #7878

[robert3005]

and here I thought this is more complicated

[codspeed-hq]

Merging this PR will improve performance by 19.48%

⚠️ 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.

⚡ 9 improved benchmarks
✅ 1201 untouched benchmarks

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	encode_varbin[(1000, 2)]	167.7 µs	146.6 µs	+14.42%
⚡	Simulation	encode_varbin[(1000, 32)]	169.6 µs	153 µs	+10.83%
⚡	Simulation	encode_varbin[(1000, 4)]	163.7 µs	147.2 µs	+11.27%
⚡	Simulation	encode_varbin[(1000, 8)]	164.5 µs	147.9 µs	+11.17%
⚡	Simulation	patched_take_10k_dispersed	317.9 µs	288.1 µs	+10.36%
⚡	Simulation	patched_take_10k_first_chunk_only	304.2 µs	274.4 µs	+10.89%
⚡	Simulation	patched_take_10k_adversarial	260.8 µs	230.9 µs	+12.98%
⚡	Simulation	take_10k_first_chunk_only	272.6 µs	228.2 µs	+19.48%
⚡	Simulation	take_10k_dispersed	286.3 µs	241.8 µs	+18.4%

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_{Comparing ji/like-get-item-get (38efa22) with develop (93d0b4e)}