Add bound expression rewrite optimizer

[mhk197]

Summary

• add a deterministic bottom-up optimizer for bound expressions
• preserve expression dtypes across rewrites and reject invalid or unchanged replacements
• organize built-in rewrites by binary, cast, structural, null, and conditional families

Changes

• add a reusable BoundExpressionOptimizer with ordered rule registration and a rewrite-cycle budget
• use a per-invocation OptimizationRun with small inline task and result stacks
• rebuild parent nodes only when an optimized child changed
• mirror the existing scalar-function simplify and reduce behaviors with bound-expression rules
• document the optimizer state machine and every built-in rewrite with original and rewritten examples

Testing

• cargo test -p vortex-array expr::optimizer
• cargo test --doc -p vortex-array
• cargo clippy --all-targets --all-features
• cargo +nightly fmt --all -- --check
• git diff --check

[codspeed-hq]

Merging this PR will improve performance by 30.63%

⚠️ Unknown Walltime execution environment detected

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⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
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⚡ 3 improved benchmarks
✅ 445 untouched benchmarks
⏩ 1770 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	WallTime	arrow_checked_add_u32_neon[16384]	20.4 µs	12.4 µs	+65.02%
⚡	WallTime	arrow_checked_add_u32_avx512[16384]	21.3 µs	17.6 µs	+20.67%
⚡	WallTime	mul_u32_nonnull_avx512	6.3 µs	5.6 µs	+11.94%

Tip

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

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_{Comparing mk/bound-expression-optimizer (83e8bba) with develop (ee1ac25)}

Footnotes

1. 1770 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩