078 reject redundant when parens

// ============================================================================
// Test 210_078: MUST_FAIL — outer parens wrapping the whole `when` condition
//                          are redundant and rejected.
//
// `when` already delimits the expression; the outer parens add no information
// and visually echo C-family `if (cond)` syntax that Koru does not adopt.
// Inner parens for sub-expression grouping (`when foo == (a + b)`) remain
// legal — only whole-expression wrapping is rejected.
// ============================================================================

~event check { x: i32 }
| high i32

~check(x: 5)
| high h when (h > 10) |> _
| high _ |> _