Decompose TurboQuant into 2 ScalarFnArrays and DictArray (#7374)

## Summary

Tracking issue: #7297

Decomposes `TurboQuant` into:

```text
ScalarFnArray(L2Denorm, [
    ScalarFnArray(SorfTransform, [
        Extension<Vector>(
            FixedSizeListArray(
                DictArray(codes=Primitive<u8>, values=Primitive<f32>),
                padded_dim
            )
        )
    ]),
    norms
])
```

This makes the implementation more modular and turns the
TurboQuant-specific pieces into reusable building blocks.

Also defines SORF sign generation with a frozen local `SplitMix64`
implementation and cleans up related vector compute code.

## API Changes

- add `SorfTransform`
- remove the `TurboQuant` encoding/array type
- keep `TurboQuantScheme` as the compressor entry point
- simplify a all scalar fn APIs as we no longer need `ApproxOptions`

Note that `ApproxOptions` doesn't actually make sense here because we
are doing exact compute here, it is the encoding itself that is lossy.
Until we figure out what the exact semantics are of a lossy encoding I
will remove this.

## Testing

More tests:
- TurboQuant roundtrip / structural coverage
- SORF roundtrip + norm preservation
- deterministic SplitMix64 / sign generation coverage
- readthrough behavior (when children are normalized) for vector
similarity ops

---------

Signed-off-by: Connor Tsui <connor.tsui20@gmail.com>
Co-authored-by: Claude <noreply@anthropic.com>

Author: connortsui20

vortex-file/src/strategy.rs

@@ -56,8 +56,6 @@ use vortex_pco::Pco;
 use vortex_runend::RunEnd;
 use vortex_sequence::Sequence;
 use vortex_sparse::Sparse;
-#[cfg(feature = "unstable_encodings")]
-use vortex_tensor::encodings::turboquant::TurboQuant;
 use vortex_utils::aliases::hash_map::HashMap;
 use vortex_utils::aliases::hash_set::HashSet;
 use vortex_zigzag::ZigZag;
@@ -111,8 +109,6 @@ pub static ALLOWED_ENCODINGS: LazyLock<HashSet<ArrayId>> = LazyLock::new(|| {
     allowed.insert(RunEnd.id());
     allowed.insert(Sequence.id());
     allowed.insert(Sparse.id());
-    #[cfg(feature = "unstable_encodings")]
-    allowed.insert(TurboQuant.id());
     allowed.insert(ZigZag.id());
 
     #[cfg(feature = "zstd")]

vortex-tensor/Cargo.toml

@@ -29,8 +29,8 @@ half = { workspace = true }
 itertools = { workspace = true }
 num-traits = { workspace = true }
 prost = { workspace = true }
-rand = { workspace = true }
 
 [dev-dependencies]
+rand = { workspace = true }
 rand_distr = { workspace = true }
 rstest = { workspace = true }

vortex-tensor/public-api.lock

@@ -4,7 +4,6 @@
 //! Encodings for the different tensor types.
 
 // TODO(connor):
-// pub mod norm; // Unit-normalized vectors.
 // pub mod spherical; // Spherical transform on unit-normalized vectors.
 
 pub mod turboquant;