[APP-736] fix: default filters producing array-wrapped values in IN/NIN expressions

[briangregoryholmes]

• The Go backend's filter parser creates IN/NIN expressions with array-valued entries (e.g. { val: ["Name"] }) instead of individual value expressions ({ val: "Name })
• When serialized to a filter string this produces username NIN (['Name']) instead of username NIN ('Name'), which fails when sent to the API
• Apply flattenInExpressionValues in getFiltersFromText and flattenExpression to normalize array-valued IN/NIN expressions at both entry points

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!

[ericokuma]

Thanks Brian! LGTM!

[AdityaHegde]

nit: remove log