add default timeout environment variable RSTEST_TIMEOUT

[aviramha]

closes #190
I didn't add tests because I wasn't sure how to test it - would love guidance.

[la10736]

The implementation it's OK. Can you also update changelog.md and the docs in

rstest/rstest_macros/src/lib.rs

Line 757 in 2f1ff25

/// ### Test `#[timeout()]`

? I 've this duplication to handle by now.... I'll switch to cargo-readme soon.

For integration test look at

rstest/rstest/tests/rstest/mod.rs

Line 919 in 2f1ff25

fn timeout() {

but you need to modify the framework in rstest_test also to inject environment variable.
There are no unit tests about timeout rendering but in this case what you would to test is the environment injection logic (like a singleton) so the integration test should be enough.

[aviramha]

thank you, added tests.

[la10736]

Ok, fine to me. I'll do the bureaucracy 😄