Bug description

SimpleVectorStoreFilterExpressionConverter has a bug when converting filter expressions.
When a metadata key contains the substring "in", the converter mistakenly interprets it as an IN operator because it checks:

Expected Behavior

When converting a filter expression where:

• the operator is EQ
• the metadata key contains "in" as a substring
• the value is a List

the converter should output a standard SpEL equality expression.

Filter.Expression expr = new Filter.Expression(
    ExpressionType.EQ,
    new Filter.Key("pin code"),
    new Filter.Value(List.of("1234", "5678"))
);

The expected SpEL output is:

#metadata['pin code'] == {'1234','5678'}

Current Behavior

The current SimpleVectorStoreFilterExpressionConverter incorrectly interprets the key substring "in" as the IN operator because it checks:

context.lastIndexOf("in")

As a result, the converter generates an unintended contains() expression

{'1234','5678'}.contains(#metadata['pin)

This is invalid and breaks metadata filtering in SimpleVectorStore.

Proposed Fix

Modify the doValue() implementation to distinguish real IN operators from accidental key substrings

String ctx = context.toString().trim();
boolean isInClause = ctx.endsWith(" in");
boolean isNotInClause = ctx.endsWith(" not in");

if (!isInClause && !isNotInClause) {
    context.append(formattedList);
} else {
    appendSpELContains(formattedList, context);
}

This ensures substring "in" inside a metadata key is not mistaken for the IN operator.