gh-146256: Add --jsonl collector to the profiling.sampling

[maurycy]

This PR adds --jsonl discussed in #146256.

It's a draft - it does not contain tests yet. The class is below 2**8 lines of code and does not touch existing profiling.sampling code, so I took a leap. I'm already very uncomfortable with creating a PR for an issue that wasn't discussed. I don't want to clutter it with tests, until the format is solidified.

For example:

sudo -E \
  uv run \
    --python /Users/maurycy/src/github.com/maurycy/cpython/python.exe \
      python \
        -m profiling.sampling \
           run \
             --jsonl \
             -o /tmp/profile.jsonl /tmp/hello_world.py

Where /tmp/hello_world.py could be:

import time
print("Hello, World!")
time.sleep(0.1)

Given the similarity, the class just inherits from StackTraceCollector. (I think this is a good hint that the collectors should be separate from renderers.)

Visual Studio Code Extension

For the purpose of demonstrating the --jsonl usefulness, I have vibe-coded (with Claude Code) a simple VSCode Extension (only that) that leverages this play profile and displays it in the editor:

I think that, once we have --stream it will be much more exciting.

Apart from headless profilers: updating the real-time hot spots from the production in VSCode, or, well, making agents' life easier.

You can fetch the vibe-coded VSCode Extension here (no guarantees):

• https://gist.github.com/maurycy/50a80586636a90216efc86065bbfd6de
• https://gist.github.com/maurycy/fa4c3acd9e8e681a609bddc9ad04c4ae

Or:

mkdir -p ~/.vscode/extensions/profiling-heatmap                                                                                                                                                                                   
curl -sL 'https://gist.githubusercontent.com/maurycy/50a80586636a90216efc86065bbfd6de/raw/719e46f4f086c819edbbee7b20c45c41eae15e8b/extension.js' -o ~/.vscode/extensions/profiling-heatmap/extension.js                           
curl -sL 'https://gist.githubusercontent.com/maurycy/fa4c3acd9e8e681a609bddc9ad04c4ae/raw/1edd3c2716a4a9e55aba8ed94850fd70f61fa606/package.json' -o ~/.vscode/extensions/profiling-heatmap/package.json                           
echo "Restart VSCode, then: Cmd+Shift+P -> 'Profiling: Load JSONL Profile'"   

Please do not forget about removing ~/.vscode/extensions/profiling-heatmap/ after tests.

• Issue: Add --jsonl flag to the profiling.sampling #146256

[pablogsal]

@ivonastojanovic can you take a look?

[maurycy]

@ivonastojanovic @pablogsal Thank you.

Please note that I've started adding test coverage, so it might be worth waiting a day with a proper review (it's already interesting: confused myself with skip_idle), if you find the direction promising.

I will mark it as Ready for review immediately.

Perhaps #146256 and #145464 are the best places to discuss the format and the ideas.