feature: TableStrategy

[a10y]

Extracting this out of my hack week project. This adds a new TableStrategy that is like the StructStrategy, except that it allows users to override the write strategy at particular field paths in the schema.

For example, if you have a schema like this:

request: struct?
|__ id: utf8
|__ duration_ms: i64
|__ body: struct?
	|__ bytes: binary?
    |__ json: utf8?

Before you'd be stuck with choosing a single strategy for all fields of the Struct.

TableStrategy allows you to override particular field paths anywhere in the field tree. For example, if you wanted to allow uncompressed struct validity, default BtrBlocks compression but ZSTD compression just for the request.body.bytes field, you'd do:

let btrblocks = Arc::new(CompressingStrategy::new_btrblocks(FlatLayoutStrategy::default()));
let zstd = Arc::new(CompressingStrategy::new_compact(FlatLayoutStrategy::default()));

let table_strategy = TableStrategy::new(
            FlatLayoutStrategy::default(), 
            btrblocks,
        )
        .with_leaf_strategy(field_path!(request.body.bytes), zstd);

I've replaced StructStrategy with this in the default WriteBuilder.

If we like this, we might want to consider marking StructStrategy as deprecated.

[codecov]

Codecov Report

❌ Patch coverage is 89.16667% with 26 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.39%. Comparing base (374882d) to head (11a8904).
⚠️ Report is 22 commits behind head on develop.

Files with missing lines	Patch %	Lines
vortex-layout/src/layouts/table.rs	87.23%	18 Missing ⚠️
vortex-file/src/strategy.rs	38.46%	8 Missing ⚠️

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[gatesn]

Yeah really nice idea. Definitely should just immediately deprecate the StructStrategy.

[gatesn]

Is this only for non-leaf struct validity? Or all validity? Do we just need a special type of FieldPath that allows us to index into the nulls etc?

e.g. enum PathComponent { Field(FieldName), ListElements, Validity } maybe? Not sure... might be gross.

[a10y]

structs are the only case right now where validity is extracted out and compressed into its own child layout, all of the other strategies just store it alongside the array data

[gatesn]

Yeah, I think you actually want to check the leaf_writers here for a root FieldPath, that would allow overriding intermediate struct strategies.

[a10y]

This is actually to maintain compatibility with behavior in StructStrategy, which lets you serialize non-struct flat arrays. Not sure why we let you do that but it's the current behavior and we have unit tests for it 🤷

[AdamGS]

nit - 58 is the latest release

[AdamGS]

nit - rustdoc

[AdamGS]

LGTM, a big part of this is pulled from StructLayout

addressed