test: add tests on linux/arm64, macOS, nightly

[reubeno]

Taking inspiration from #23, expands PR/CI testing via matrix:

• Adds build-only validation on 1.65.0 (see below)
• Adds test validation on 1.71.0, stable, and nightly (x86_64/Linux)
• Adds test validation on arm64 Linux (stable)
• Adds unit-test-only validation on macOS (stable)

Also adds 2 basic integration tests for all_users and all_groups.

---

Notes:

• Regarding min Rust versions, I used cargo msrv to empirically compute the effective MSRV of this crate as 1.65.0. I then discovered that the dev dependency on env_logger for testing raises the minimum for testing as being 1.71.0. I ended up adding both to the matrix, disabling test execution on the older version.

• On macOS, libnss_wrapper doesn't appear available so I've only enabled unit tests there until an alternate strategy could be adopted.

Potential future work:

• Formally document MSRV via metadata in Cargo.toml.
• At least validate build for alternate targets (e.g., BSD families) using cross or cargo --target.
• Explore use of vmactions GitHub actions for running build-and-test on alternate OSes using VMs hosted in PR/CI workflows.

[reubeno]

Hi @gierens -- I've posted this PR as an attempt to contribute toward issue #23. This would be my first contribution to this project, and I'd be grateful for any feedback you'd have.

Thanks!

[gierens]

Hi @reubeno,

Sorry for the late reply, I've been quite busy the last couple of weeks. Anyway, thanks for this clean and well documented PR. LGTM! One minor thing, since the added tests are an unrelated change, I split this into two commits.

Regarding future work, yeah, documenting the MSRV is a good idea. As for testing on other targets, yeah, we are using vmactions on eza, too.

[reubeno]

No worries! Splitting the commits makes total sense. Thanks for merging it 😄

Thanks also for the pointer to eza's use of vmactions. Doing something similar sounds like a reasonable follow-up step at some point.