Fix stack overflow on deeply-nested JSON in json.loads() by changjoon-park · Pull Request #7632 · RustPython/RustPython

json.loads() on a deeply-nested array or object payload (e.g.
'[' * 50000 + ']' * 50000) overflowed the native Rust stack and
crashed the interpreter process with SIGSEGV. CPython raises
RecursionError on the same input via _Py_EnterRecursiveCall in
Modules/_json.c.

The recursion lives in the mutual call chain:
  JsonScanner::parse_object / parse_array
    -> JsonScanner::call_scan_once
      -> JsonScanner::parse_object / parse_array

Every descent funnels through call_scan_once, so wrapping its body
with vm.with_recursion covers both '{' and '[' paths (and their
mixed nesting) with a single guard.

Before:
  ./rustpython -c "import json; json.loads('[' * 50000 + ']' * 50000)"
    -> SIGSEGV (exit 139)

After:
  -> RecursionError: maximum recursion depth exceeded while
     decoding a JSON object from a string

Verified:
  - extra_tests/snippets/stdlib_json.py: all assertions pass
    (includes 3 new regression cases: array, object, alternating
    nesting at depth 100000)
  - cargo run -- -m test test_json: 214 passed, 0 regressed
    (9 skipped, 13 expected failures, all pre-existing)
  - depth 500000 no longer crashes (RecursionError)
  - shallow parsing unchanged

Per @ShaharNaveh's review on RustPython#7632: this test was previously marked
`@unittest.skip("TODO: RUSTPYTHON; crashes")` because json.loads
would SIGSEGV on the 500_000-deep input. The recursion-guard added
in this PR makes it raise RecursionError like CPython, so the skip
decorator can be removed.

  $ cargo run -- -m unittest \
        test.test_json.test_recursion.TestCRecursion.test_highly_nested_objects_decoding \
        test.test_json.test_recursion.TestPyRecursion.test_highly_nested_objects_decoding
  ...
  Ran 2 tests in 0.825s
  OK

  $ cargo run -- -m test test_json
  Ran 214 tests (7 skipped, 13 expected failures) — all pass.