CommonJS model: comment and doc-comment slips in the shape gate #39

Found in the round-1 review of branch fix/commonjs-model-gaps (stacked on PR #29).

1. The expandEvals comment says the gate expands a literal eval the same way the model does. It doesn't: the gate splices {payload} as a block, and the model wraps it in (()=>{payload})(). var and function declarations are scoped differently in the two forms. Either use the same splice in both places or fix the comment.
2. CODE_RUNNERS/TIMERS (and ARRAY_FILLS) were inserted between the /** Unknowns the model answers as blocked … */ doc comment and BLOCKING_UNKNOWNS. The doc comment now attaches to CODE_RUNNERS. Move the new constants above it.