fix(spark): array_contains compares floats the way Spark does - #83

Which issue does this PR close?

• Addresses the float equality difference in spark: array_contains compares floats by bits, where Spark treats -0.0 as 0.0 and all NaNs as equal #34. The untyped NULL argument difference mentioned in the comments there is not changed by this PR, so I left the issue open.

Rationale for this change

array_contains delegates the element comparison to array_has, which compares floating point values by their bits. Spark compares them with -0.0 == 0.0 and NaN == NaN: CodegenContext.genEqual in Spark 4.2.0 generates (java.lang.Double.isNaN(c1) && java.lang.Double.isNaN(c2)) || c1 == c2 (and the same for Float).

So array_contains(array(-0.0D), 0.0D) returned false here and true in Spark, and two NaNs with different sign bits or payloads did not match, at any depth of list and struct elements.

What changes are included in this PR?

• array_contains.rs rewrites the float values of both arguments before calling array_has: -0.0 becomes 0.0 and every NaN becomes the canonical NaN. It applies to scalar and array arguments, and to Float32/Float64 at any depth of List, LargeList, FixedSizeList and Struct. Arrays that hold no floats are returned as they are. The existing null handling is unchanged.
• FixedSizeList is rebuilt with try_new_with_length, so a zero-width list keeps its rows.
• array/array_contains.slt: new queries for both zeros in both directions (double and float), NaN with a flipped sign bit, LargeList and FixedSizeList haystacks, nested lists and structs, null semantics, and a table with column arguments.
• Unit tests in array_contains.rs for the normalization (scalar and nested shapes, zero-width lists, reuse of children without floats).

An earlier attempt at this issue, apache/datafusion#26011, was closed before the move. Its review asked for a length-preserving rebuild of zero-width FixedSizeList and tests for it, which this PR includes.

What is the testing strategy for this PR?

• cargo fmt --all -- --check, cargo clippy --all-targets --all-features -- -D warnings, cargo test -p datafusion-spark (331 passed) and cargo test -p datafusion-spark-sqllogictest (245 of 245 files) pass.
• With array_contains.rs from main, the new float queries fail. Run one by one, 9 of 14 probe queries fail on main (top-level -0.0, NaN with a flipped sign bit at every depth, LargeList/FixedSizeList); nested -0.0 already compares equal on main and is kept as a guard.
• Each branch of the new code is covered by at least one test that fails when the branch is removed (checked by hand: no normalization, NaN branch, zero branch for f32 and f64, struct, list, scalar path, zero-width length, early return).

Unknowns and assumptions

• I could not run Spark here. The expected values come from Spark's source (genEqual, 4.2.0) and from the report in spark: array_contains compares floats by bits, where Spark treats -0.0 as 0.0 and all NaNs as equal #34, not from a live PySpark session.
• arrays_overlap (mentioned in spark: array_contains compares floats by bits, where Spark treats -0.0 as 0.0 and all NaNs as equal #34) is not touched.

Are there any user-facing changes?

array_contains on float or double elements now matches Spark for -0.0 and NaN. No API change.