fix: allow use of a list of values for field filtering, and format

[jwilkinson87]

This pull request enhances the flexibility and correctness of filter expression formatting in the request router. The main improvements are the addition of support for list values in field filters, improved quoting for string values, and new tests to ensure correct filter formatting, especially for lists and logical expressions.

Filter expression improvements:

• Updated FieldFilterExpression to support values of any type, including lists, and to properly quote string values and handle nulls. This allows filters like field('a','b','c') to be generated when a list is provided.

Testing enhancements:

• Added tests to verify that FieldFilterExpression formats lists of values correctly in the filter string.
• Added tests to ensure that logical expressions like OrExpression work correctly with both list and single field filters, verifying their combined formatting.

Code quality:

• Added @Suppress("unused") to the OrExpression class to prevent warnings about unused code, improving code clarity.

[github-actions]

There is a problem with the Gemini CLI PR review. Please check the action logs for details.