Reduce status checks

[fuzzypixelz]

In GitHub repository settings, the "Require status checks to pass before merging" branch protection rule ensures that commits are only merged from branches where specific status checks have passed. These checks are specified manually as a list of workflow job names.

To properly use the branch protection rule, we need this additional 'all encompassing' status check. Without this, GitHub won't wait for status checks when auto-merging pull requests.

Further context and a more feature-full implementation is available at: https://github.com/re-actors/alls-green. Although we don't (currently) need an 'allow skips' or 'allow failures' option so the value of adding yet another dependency is questionable.

Needless to say, this change needs to be propagated to all other eclipse-zenoh/zenoh-* repositories. We could add this logic in an action under .github/actions/reduce-status-checks.yml and use that from the other repositories. However, all we would factor out is the jq command (and maybe the comment/documentation). This makes for a good argument for using the existing re-actors/alls-green action.

[fuzzypixelz]

When running tests, the cargo install nextest step takes 5-8mins, which is nearly half the time is takes for the tests themselves to run. I switched to using pre-built binaries.

[fuzzypixelz]

I removed the nightly requirement for nostd-check as it's no longer necessary. Moreover, now the nostd-check binary runs on Ubuntu/Windows/macOS instead of just Ubuntu as part of the check job.

The last commit status fails due to a spurious test failure, even though it was a simple workflow step name change. When we do enable branch protection these kind of failures might become an issue.