feat: add an arrays slots macro

[joseph-isaacs]

Adds a array_slot(VTable) attr macro which can be applied to a slots struct. This gives types access to the slots for an array.

e.g.

#[array_slots(ALP)]
pub struct ALPSlots {
    /// The ALP-encoded values array.
    pub encoded: ArrayRef,
    /// The indices of exception values that could not be ALP-encoded.
    pub patch_indices: Option<ArrayRef>,
    /// The exception values that could not be ALP-encoded.
    pub patch_values: Option<ArrayRef>,
    /// Chunk offsets for the patch indices/values.
    pub patch_chunk_offsets: Option<ArrayRef>,
}

[codspeed-hq]

Merging this PR will not alter performance

✅ 1122 untouched benchmarks
⏩ 1530 skipped benchmarks¹

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_{Comparing ji/array_slots-macro (954250e) with develop (c660607)}

Footnotes

1. 1530 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. ↩

[robert3005]

@connortsui20

[connortsui20]

just at a quick glance, I think it is super important that we have documentation that explains what gets generated, instead of having to read to proc macro code

[robert3005]

Fair, I had to review with an ide to see macro expansions

[joseph-isaacs]

I am happy to add just wanted to see what is was and if this was the right approach?