guard recursive comparisons against stack exhaustion

[atharvmantri]

Summary

Bound recursive JSON comparisons by the existing CJSON_NESTING_LIMIT.

cJSON_Compare() recursively descends arrays and objects without a depth check, and the private comparison used by JSON Patch test and merge-patch generation has the same behavior. Deep or cyclic caller-supplied trees can therefore exhaust the native stack even though parsing, printing, and duplication already enforce recursion limits.

This change keeps the public API unchanged, threads a depth counter through the internal recursion, and returns false when the configured limit is reached. The merge-patch generator also carries the limit instead of re-entering through the public wrapper, and propagates a failed nested patch rather than silently dropping it. Both comparison paths use the existing project-wide limit rather than introducing a second policy.

Related: #1073.

Testing

• git diff --check
• Verified all recursive calls use the depth-carrying helpers, all entry points start at depth zero, and nested merge-patch failure is propagated.
• A native C compiler is not available in the submission environment, so the project test suite could not be run locally.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.