Fix `cargo miri test --all-features`

[zetanumbers]

• [x] -Zmiri-ignore-leaks baseline
• [x] -Zmiri-tag-raw-pointers
• [x] -Zmiri-strict-provenance (cargo miri --version f76ebd6 2022-07-02)
• [ ] eliminate -Zmiri-ignore-leaks

Also adds test_skip_miri_quickchecks default feature.

Fixes #166, fixes #164

[zetanumbers]

So i ran cargo miri test --test quickchecks ..., and it have spuriously failed on alloc_strs and can_allocate_big_values tests, only indicating that one of its spawned cargo miri process exited with error code 255. Could this be OOM bc of a leak?

UPDATE: running 1 quicktest on alloc_strs with leak detection enabled completes successfully.

[fitzgen]

I doubt there is a leak here, since I think valgrind (which we run tests under in CI) would have complained about that.

[fitzgen]

Thank you for your patience and for sticking with this PR!

[zetanumbers]

No problem. Sorry for the long delay.