feat: support ilike expression

[n0r0shi]

Summary

• Wire ilike from the datafusion-spark crate (SparkILike) to Comet
• Register in jni_api.rs and add serde mapping in QueryPlanSerde.scala
• Custom handler CometILike in strings.scala to reject non-default escape characters
• ILIKE requires case-insensitive comparison which depends on locale-specific case conversion. When spark.comet.caseConversion.enabled is disabled (default), ILIKE falls back to Spark to avoid incompatibilities with Rust's Unicode-based to_lowercase() vs Java's locale-aware rules (e.g. Turkish I)

Please let me know if the caseConversion handling is not appropriate