[ESQL] SingleValueQuery may stop emitting some warnings if it is cached

[iverase]

SingleValueQuery is a wrapper for lucene queries in ESQL. It wrps queries in order to emit warnings in case queries are being executed against multivalue fields. We don't fail the queries but emit warnings instead.

In #110035 we fixed the implementation of equals and hashcode, with the side effect that queries might be cached by the query cache. The side effect is that queries that emit warnings, when running agains the cached version might stop emitting those warnings which is probably not desire.

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)