fix(mkconcore): make the posix clear script empty every edge directory

[Atharvsinh-codez]

The posix clear script that mkconcore generates only empties the first edge directory.

Each edge gets a line like cd Y && rm -f *, and all of them run in the same shell. After the first line the script is still inside Y, so every later relative cd fails, its rm is skipped, and ./clear exits 1. The remaining edges keep their old data, so the next run of the study starts from stale values.

With demo/sample.graphml on dev:

#!/bin/bash
cd CU && rm -f *
cd PYM && rm -f *

./clear prints cd: PYM: No such file or directory, exits 1, and leaves everything in PYM.

This came in with 991373c (shell escaping), which replaced rm <edge>/* with the cd. I kept that approach and just run each line in a subshell, (cd CU && rm -f *), so the cd doesn't carry over. Windows (del /Q) and docker (docker volume rm) clear scripts don't cd, so they're not affected.

Changes:

• mkconcore.py: wrap each posix clear line in a subshell (one line)
• tests/test_cli.py: build a posix study with three file edges, run the generated build and clear, and check that every edge directory is empty and clear exits 0. It fails on dev and passes with this change. Skipped on Windows since it runs the bash scripts.

Verified with:

• pytest (217 passed, 4 skipped)
• built demo/sample.graphml with posix, put a file in each edge directory and ran ./clear: on dev PYM is left behind and the exit code is 1, with this change both are emptied and it exits 0
• ruff format --check . and ruff check .

I used an AI assistant to help track this down and write the test. I've reviewed the change and run everything above myself.

[github-actions]

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