🐛 Change cwd for coverage reports

[sam-mosleh]

First time installing mutmut — excited to try it out, but ran into a couple of issues on my machine that blocked me from running it at all on my MacBook running Tahoe v26.3.1. This PR fixes both:

Fix 1: Segfault on startup due to setproctitle

On macOS, mutmut crashes immediately with a segfault. After some digging, the culprit is the call to setproctitle which fails simply because forking on macOS is inherently unsafe. I want to be upfront that this may not be the right long-term fix. I went with the simplest change to unblock myself, but I'm very open to guidance from you (@boxed) on the preferred approach.

Fix 2: Coverage configuration not being respected

Even after unblocking the segfault, I noticed that coverage reports were not picking up the project's coverage configuration (e.g., .coveragerc or [tool.coverage] in pyproject.toml). For example omit configs fail to locate files because it is called from the parent mutants directory.

[Otto-AA]

Thanks, the cwd for coverage makes sense and looks good to me. Just a small nitpick there for maintainability.

The setproctitle issue is already covered by #476.

[Otto-AA]

Even after unblocking the segfault, I noticed that coverage reports were not picking up the project's coverage configuration (e.g., .coveragerc or [tool.coverage] in pyproject.toml). For example omit configs fail to locate files because it is called from the parent mutants directory.

We maybe should also add .coveragerc to the also_copy defaults

[sam-mosleh]

Thanks for the review @Otto-AA

[Otto-AA]

Thank you for the updates! Also nice that you added the small E2E test for this :)