### Rationale for this change
Our JSON parser is inherently recursive, and a crafted JSON document with huge nesting can send it into a stack overflow.
Given that real-world JSON files will not have thousands levels of nesting, we limit the JSON nesting to an arbitrary value of 300.
### Are these changes tested?
Yes, by new tests.
### Are there any user-facing changes?
**This PR contains a "Critical Fix".** A crafted JSON document with a large nesting depth could trigger a denial of service through stack overflow.
### Was AI used for this PR?
**PR code and description written by:**
- [x] Human
- [ ] AI
**Reviewed before submission by:**
- [x] Human (self-reviewed)
- [ ] AI
- [ ] Not reviewed
* GitHub Issue: #51757
Authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Antoine Pitrou <antoine@python.org>
Antoine Pitrou
c74c9576f7