experiment hypothetical “fast clone”

food for thought, hopefully this helps showcase to cost of the current cloning technique

before:

```
recast parse x 219 ops/sec ±11.90% (67 runs sampled)
acorn parse x 6,327 ops/sec ±14.49% (68 runs sampled)
esprima parse x 3,618 ops/sec ±13.15% (71 runs sampled)
```

after
```
recast parse x 1,697 ops/sec ±3.50% (79 runs sampled)
acorn parse x 7,469 ops/sec ±3.95% (79 runs sampled)
esprima parse x 4,119 ops/sec ±4.55% (70 runs sampled)
```