refactor: apply code review feedback to getCitationFieldsInputArray

[Copilot]

Addresses code review comments from PR #6738 to improve type safety, syntax, and logic in the getCitationFieldsInputArray() method.

Changes

• Added explicit return type annotation (string[]) to getCitationFieldsInputArray() for type safety
• Fixed syntax issues: removed extra space after if keyword, added missing semicolon after .split(',')
• Refined deprecation warning logic: only log warning when string value is actually provided (not for undefined)
• Added explicit fallback: return empty array when property is neither array nor string

Before

private getCitationFieldsInputArray() {
  if( Array.isArray(this.fieldsToIncludeInCitations)) {
    return this.fieldsToIncludeInCitations;
  } else {
    this.bindings.engine.logger.warn(/*...*/);
    return (this.fieldsToIncludeInCitations ?? '').split(',')
  }
}

After

private getCitationFieldsInputArray(): string[] {
  if (Array.isArray(this.fieldsToIncludeInCitations)) {
    return this.fieldsToIncludeInCitations;
  } else if (typeof this.fieldsToIncludeInCitations === 'string') {
    this.bindings.engine.logger.warn(/*...*/);
    return this.fieldsToIncludeInCitations.split(',');
  } else {
    return [];
  }
}

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