Fix `Normalized` encoding existing issues

[connortsui20]

Direction is right: this is a physical decomposition, not a scalar function. Two real wins — slice/filter push-down now always fires, and both HACK TO SUPPORT L2 DENORMALIZATION cases leave CascadingCompressor. I verified the hack removal is safe: L2Denorm was the only scheme producing an AnyScalarFn.

Items 1, 2, and 4 also reproduce on develop — they're pre-existing, not regressions from this PR. But this PR rewrites each of those code paths, so it'd be nice to fix them here rather than leave them behind the rename.

1. Panic on nullable constant norms — execute.rs:100-113

The new dtype guard blocks nullable-norms + non-nullable-child, but not both nullable. norm.clone() stays nullable, the multiply widens the FSL elements, and tensor storage elements must be non-nullable:

Unable to create `ExtensionArray`:
  Other error: Tried to create an `ExtensionArray` with an incompatible storage array

Build scale from a non-nullable copy of the scalar. A test alongside nullable_constant_norms_widen_the_decoded_dtype with the nullable-normalized-child variant would pin both halves.

2. L2Norm errors on a valid array — l2_norm.rs:131-136

norm_dtype takes its nullability from the parent (the union of both children), but the read-through returns the norms child unchanged and asserts exact dtype equality. When the parent's nullability comes from the normalized child — exactly the shape serde_round_trip_preserves_normalized_nullability builds — it fails:

Assertion failed error: norms.dtype() != &norm_dtype:
  Primitive(F64, NonNullable) != Primitive(F64, Nullable)

Widen the norms to norm_dtype instead of erroring.

3. try_new accepts a zero row paired with a non-zero norm — validate.rs:158-175

Only the stored_norm == 0.0 ⟹ all-zero row direction is checked. normalized = [0.0, 0.0] with norms = [5.0] is accepted by the checked constructor, decodes to [0.0, 0.0], but L2Norm read-through returns 5.0. try_new is documented as the constructor that makes the split lossless, and this state isn't. Add the symmetric vortex_ensure! plus an rstest case mirroring nonzero_row_with_zero_norm.

4. NormalizedScheme::matches accepts non-float tensors — compress.rs:57-63

matches only checks ext_dtype().is::<AnyTensor>(), but compress calls validate_tensor_float_input. An i32 tensor column aborts the entire compression rather than falling through to another scheme:

integer tensor compression ERRORED: Other error: expected a float element dtype, got i32

matches should also require a float element ptype. This is what stands between the scheme and ALL_SCHEMES, which is the stated goal of making it compete on measured size like every other scheme.

5. Smaller items

• Grammar from the rename: "An [Normalized]" appears 8 times — array.rs:37,80,93,128, compress.rs:140,195, mod.rs:6, cosine_similarity.rs:120.
• validate_l2_normalized_rows_against_norms is the one public name left on the old naming scheme.
• The edition added list is no longer alphabetical: inner_product, normalized, l2_norm.
• Commit 1's message says "Neither constructor is unsafe", which the final code contradicts. Keeping unsafe fn new_unchecked is right — it matches FixedSizeListArray::new_unchecked — so just reword on squash.
• scalar_at inherits the constant-norms tolerance: a row whose norm is within unit_norm_tolerance of 1.0 comes back unscaled, while the bulk execute path multiplies exactly. The gap is ~ε relative, but it's a per-row semantic the bulk path doesn't have.

Checks run

Check	Result
cargo nextest run -p vortex-tensor	166 passed
cargo nextest run -p vortex-compressor -p vortex-btrblocks	89 passed, 1 skipped
cargo clippy -p vortex-tensor -p vortex-compressor --all-targets --all-features	clean
cargo +nightly fmt --all -- --check	clean

Findings 1–4 were each confirmed with throwaway probe tests in a scratch worktree; 1, 2, and 4 were re-run against develop to confirm they pre-date this PR. Not run: workspace-wide tests, Python/Java bindings, docs.

Originally posted by @robert3005 in #9138 (comment)