profiling: flamegraph export fails with RecursionError on a deeply recursive program

Bug report

Bug description:

The sampling profiler's flamegraph export (profiling.sampling.stack_collector.FlamegraphCollector.export) builds the flamegraph tree with a recursive walk (convert_children) and then serializes it with json.dumps — both recurse to the depth of the deepest sampled stack. The remote unwinder captures up to MAX_FRAMES (1536) frames, but export runs at the default recursion limit (1000), so profiling a program that recurses deeper than ~1000 makes export() raise RecursionError and write no flamegraph. Both --flamegraph and --diff-flamegraph are affected (the diff collector inherits export).

Reachable when profiling a program that raised its own recursion limit and recurses deeply (recursive-descent parsers, tree/graph walkers, deep serializers).

CPython versions tested on:

CPython main

Operating systems tested on:

Linux, macOS

Linked PRs

• gh-156546

从 profiling/sampling/stack_collector.py 中的 FlamegraphCollector.export 及其 convert_children 遍历开始。使用递归深度很深且递归限制超过所捕获堆栈深度的程序进行复现，同时使用 --flamegraph 和 --diff-flamegraph。完成的标准是两个导出路径都能生成 flamegraph，且不会出现 RecursionError；查看已链接的 PR gh-156546，了解已经在进行的工作。