Parser crashes on deeply nested input

Deeply nested Jsonnet input causes a stack overflow in the recursive descent
parser, since there is no depth limit on parse() calls.

```
python3 -c "print('(' * 100000 + '1' + ')' * 100000)" > crash.jsonnet
jsonnet crash.jsonnet
# fatal error: stack overflow
```

Reproduce the crash with the provided command and locate the recursive descent parser entry point where parse() calls accumulate. Trace how deeply nested Jsonnet input is handled, then add regression coverage for the 100,000-level case and verify that jsonnet no longer crashes with a stack overflow.

Written by the indexing model from the issue text.