Preserve NaN semantics for floating-point array_position pushdown

[fallintoplace]

Overview

Fix array_position() pushdown for real[] and double precision[] columns.

ClickHouse indexOf() can miss a NaN when the array value and the search value were produced independently. PostgreSQL treats those values as a match for array_position(), so the existing pushdown could return NULL incorrectly.

Implementation

• Keep the existing nullIf(indexOf(...), 0) path for non-floating-point arrays.
• Use arrayFirstIndex() with an explicit predicate for floating-point arrays.
• Match ordinary values, NULL, and any NaN payload.
• Qualify captured columns with the generated relation alias so lambda parameters cannot shadow outer columns such as x.
• Emit NaN, Infinity, and -Infinity constants as ClickHouse numeric float literals.
• Preserve positive start handling with arraySlice() and restore the original PostgreSQL position.

The floating-point predicate is equivalent to:

nullIf(
    arrayFirstIndex(
        value -> (
            (isNull(value) AND isNull(r1.needle))
            OR (value = r1.needle)
            OR (isNaN(value) AND isNaN(r1.needle))
        ),
        r1.float_array
    ),
    0
)

Regression coverage

• Float32 and Float64 arrays
• Ordinary matches and missing values
• Independently produced NaNs with different payloads
• A captured column named x, matching the lambda parameter name
• NaN, positive infinity, and negative infinity constants
• Positive start positions and empty arrays
• Nullable elements and NULL needles, including exact returned positions
• Generated remote SQL and relation qualification

Related issue

ClickHouse/ClickHouse#113169 tracks the underlying floating-point NaN matching behavior in ClickHouse.

Follow-up fix

The follow-up commit also covers array_position() expressions used only in pushed-down ORDER BY pathkeys. These expressions are resolved after the base relation is emitted, so they now share the same pathkey resolver during alias preflight and SQL generation. This keeps captured columns qualified in cases such as ORDER BY array_position(float64_vals, x), id.

Added regression coverage for the ORDER BY path and qualified generated SQL.

[theory]

Partial review, more later.

[theory]

Use case-insensitive comparisons