Fix: allow function calls in op is expressions

[Copilot]

Function calls returning Operation could not be used directly in op is — the compiler reported "A value cannot be used as a type." An intermediate alias was required as a workaround.

// Before: required workaround
alias T = reorderParameters(Employees.move, #["a", "b"]);
op test is T;

// After: works directly
op test is reorderParameters(Employees.move, #["a", "b"]);

Changes

• Parser: op is now uses parseCallOrReferenceExpression() instead of parseReferenceExpression(), accepting both type references and function calls
• AST (types.ts): OperationSignatureReferenceNode.baseOperation widened to TypeReferenceNode | CallExpressionNode
• Name resolver: Guards added to skip static symbol resolution for CallExpressionNode (results are dynamic)
• Checker: checkOperationIs conditionally performs circular-reference checks only for TypeReferenceNode; CallExpressionNode flows through getTypeForNode → checkCallExpression as normal