Forge reads the genesis outfile before it is completely written. This leads to errors like the following:

```
[FAIL. Reason: setup failed: failed to parse json file: "/root/project/packages/contracts-bedrock/.testdata/genesis.json": EOF while parsing a value at line 1 column 0]
```

To fix this, this PR adds a loop at the end of the file that checks if the L2 outfile is over 8 megabytes. This is a hack - a longer term fix would be to investigate why the process Forge calls via `vm.ffi` exits prior to fully writing the file. I tried calling `Sync()` from within the Go code, but it didn't fix the issue.