fix: skip Obj/EndObj for definitions without direct captures

[zharinov]

Summary

• Skip emitting Obj/EndObj wrapper for definitions that have no direct captures
• Fixes case where A = (program (B)) with B = (expr) @x would lose B's captures

Why

When a definition only calls other definitions (no direct @name captures), wrapping it in Obj/EndObj would overwrite the called definition's result with an empty object. The called definition already handles its own scope.

Before: A's EndObj creates empty {}, losing B's {x: node}
After: A has no wrapper, B's result passes through correctly