Optimizer: Unwrap CAST/SAFE_CAST in binary comparisons to enable filter pushdown (Spark parity)

Summary
Implement an optimizer rule equivalent to Spark SQL’s “UnwrapCastInBinaryComparison” to remove redundant CAST/SAFE_CAST on the column side of binary comparisons. This allows predicates to be pushed down as normal FILTERs instead of SCRIPTs.

Motivation / Problem
During Calcite validation, mismatched types can introduce SAFE_CAST on the attribute side (e.g., SMALLINT column vs INTEGER literal). This causes SCRIPT-based pushdown and prevents efficient filter pushdown.

Concrete example

• Work item surfaced in PR #4892.
• ClickBench q2: AdvEngineID (SMALLINT) compared to 0 (INTEGER) ends up as SAFE_CAST(AdvEngineID) <> 0 which becomes a SCRIPT in pushdown rather than a FILTER.

Desired behavior (high-level)

• When a binary comparison has CAST/SAFE_CAST on the column side and a foldable literal on the other side, unwrap the cast from the column and, if needed, cast the literal to the column’s type.
• Preserve null semantics appropriately (e.g., add isNotNull(col) where required by the comparison semantics).
• Result: comparisons like SAFE_CAST(col) <> 0 become col <> SMALLINT(0), enabling FILTER pushdown (no script).

Scope (initial)

• Operators: =, <>, <, <=, >, >=, BETWEEN, IN (scalar/tuple), and relevant IP variants where applicable.
• Only when one side is CAST/SAFE_CAST of an attribute (or a simple expression derived from it) and the other side is a literal/foldable.
• Do not change behavior in cases that would alter correctness (e.g., overflow/precision edge cases without a safe equivalent).

References

• Spark optimizer rule: UnwrapCastInBinaryComparison
  https://github.com/apache/spark/blob/master/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/UnwrapCastInBinaryComparison.scala

Backlinks

• PR: https://github.com/opensearch-project/sql/pull/4892
• Comment: https://github.com/opensearch-project/sql/pull/4892#discussion_r2730526656

Acceptance criteria

• Predicates that currently generate SCRIPT pushdown solely due to CAST/SAFE_CAST on the column side are rewritten to enable FILTER pushdown.
• No regressions in correctness; add integration coverage (e.g., ClickBench q2) demonstrating the switch from SCRIPT to FILTER pushdown.
• Document the rule and any corner cases (null handling, overflow behavior) in developer docs.

Requested by
@LantaoJin