Instead of trying to handle signals for every step of the `cursive`
event loop, move the signal handling into its own asynchronous task and
send callbacks to `cursive` when a signal arrives.
The `lazy_static` crate was superseded by the `once_cell` crate which
has been included in Rust's standard library since version `1.70`.
Remove the `lazy_static` dependency and refactor all use cases to use
`std::sync::OnceLock` instead.
Co-authored-by: Henrik Friedrichsen <henrik@affekt.org>
To have a clear distinction between code dealing with OS process
characteristics and code of ncspot itself, it makes sense to move the
async runtime together with ncspot as it doesn't have anything to do
with the OS process.
Some applications move their 'global' data into a struct called `App` or
`Application`. This makes it very clear what data belongs to the
'global' scope or in other words, to the application itself.
