fix(executor): include arguments in aggregate column names

Issue #6: getSelectColumns() produced count() for count(*)
and max() for max(id). Now uses exprToSql() on funcArgs
to generate consistent names matching the actual SQL expression.

Before: columns: @[count()], rows: @[{count(*): 2}]
After:  columns: @[count(*)], rows: @[{count(*): 2}]

src/barabadb/query/executor.nim

@@ -2678,7 +2678,10 @@ proc getSelectColumns(stmt: Node): seq[string] =
     elif e.kind == nkPath and e.pathParts.len > 0:
       result.add(e.pathParts[^1])
     elif e.kind == nkFuncCall:
-      result.add(e.funcName & "()")
+      var aliasArgs: seq[string] = @[]
+      for arg in e.funcArgs:
+        aliasArgs.add(exprToSql(arg))
+      result.add(e.funcName & "(" & aliasArgs.join(", ") & ")")
     elif e.kind == nkStar:
       result.add("*")
     else: