088 reject redundant punning call site

// ============================================================================
// Test 210_088: MUST_FAIL — explicit label `v: v` at a call site is forbidden
//                          because punning would produce the same name.
//
// The bare identifier `v`, when passed positionally, puns to `v: v` (the last
// segment of the path names the parameter). Writing the explicit label adds
// no information and is rejected at parse time. The canonical form is
// `echo(v)`.
//
// Same mechanism, same rule applies to deeper paths: `echo(v: p.q.v)` is
// rejected because `p.q.v` also puns to `v` — see 210_089.
// ============================================================================

~import std/io

~event echo { v: i32 }
| out i32

~echo => out v

~echo(v: v)
| out r |> std/io:print.ln("{{ r:d }}")