Implement optional support for axum 0.8's Listener trait

[kanpov]

Everything about this PR is mostly obvious, with the feature being named axum08 similarly to the tonic-related compat features. There is one exception, however, that being the accept error handling behavior: the Listener's accept definition is infallible and states:

/// If the underlying accept call can return an error, this function must
/// take care of logging and retrying.

I used the approach axum developers themselves used for implementing Listener for TCP and UDS listeners, more info in the handle_accept_error method that is almost a direct copy-paste from axum's internals. My assumption is that if it's considered "good enough" by axum, it should be for tokio-vsock, but I might be wrong.

[jalil-salame]

The commit message check requires this commit to have a body, you can simply summarize the issue (that this is required due to the orphan rule) and it should be fine c:

Thanks for this! Would've loved to have access to this 2 years ago!

[kanpov]

@jalil-salame Fixed and squashed!