Draft support for pprof profile.proto format

[torshepherd]

Hi, this PR adds basic draft support for pprof's profile.proto format. I wanted to put this up early before diving too deep into the details to gauge if there is appetite for upstreaming this.

Example profile for a dummy program:

SVG:

Pprof:

Pprof comes with a number of other niceties. For instance, you can view the source code:

If there is interest in upstreaming this, I have a number of other improvements I would do:

1. Render subprocess hierarchies like the other formats can
2. Collect procmaps and save memory mappings for native unwound code. This would be a massive leg up on the current status quo, as it would allow pprof to disassemble and show stack samples at the instruction level in the UI.
3. Add some batching/caching while building that should save more space in the output profile.

But already in my limited testing I'm seeing that gzipped profile.proto files are quite a bit smaller than the svg files:

Format	File	Size	Samples
pprof-gzip	/tmp/complex_native.pprof.gz	267KB	727
SVG	/tmp/complex_native.svg	981KB	669

I would also be happy to move these additional dependencies and features behind a feature flag!

Disclaimer: This PR was made with light LLM usage, mostly just asking which libraries I should use. The pprof.rs file is quite rough so if this is an acceptable direction, I would clean it up a decent amount before asking for real code review time