profiling.sampling heatmap reads non-regular and oversized files

Bug description

The heatmap exporter in profiling.sampling reads source files named in a profile unconditionally via Path(filename).read_text(). It does not check whether the path is a regular file or whether the file size is reasonable.

When replaying a binary profile, a filename pointing to a device file (e.g. /dev/zero) causes unbounded memory growth. An oversized file has the same effect.

The fix adds an is_file() guard and a 10 MB size cap before reading, consistent with the binary reader hardening in gh-152718.

CPython versions tested on

main

Operating systems tested on

macOS

Linked PRs

• gh-153839

从 profiling.sampling 热图导出器开始，该导出器使用 Path(filename).read_text() 读取源路径，并参考 gh-152718 中对二进制读取器的加固方式进行比较。完成的标准是：不读取非普通路径和超过 10 MB 的文件；gh-153839 已作为拟议工作链接。