Add and use new Signals struct (#13314)

# Description
This PR introduces a new `Signals` struct to replace our adhoc passing
around of `ctrlc: Option<Arc<AtomicBool>>`. Doing so has a few benefits:
- We can better enforce when/where resetting or triggering an interrupt
is allowed.
- Consolidates `nu_utils::ctrl_c::was_pressed` and other ad-hoc
re-implementations into a single place: `Signals::check`.
- This allows us to add other types of signals later if we want. E.g.,
exiting or suspension.
- Similarly, we can more easily change the underlying implementation if
we need to in the future.
- Places that used to have a `ctrlc` of `None` now use
`Signals::empty()`, so we can double check these usages for correctness
in the future.

crates/nu-command/src/date/humanize.rs

@@ -50,7 +50,7 @@ impl Command for SubCommand {
         if matches!(input, PipelineData::Empty) {
             return Err(ShellError::PipelineEmpty { dst_span: head });
         }
-        input.map(move |value| helper(value, head), engine_state.ctrlc.clone())
+        input.map(move |value| helper(value, head), engine_state.signals())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/date/list_timezone.rs

@@ -40,7 +40,7 @@ impl Command for SubCommand {
                     head,
                 )
             })
-            .into_pipeline_data(head, engine_state.ctrlc.clone()))
+            .into_pipeline_data(head, engine_state.signals().clone()))
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/date/to_record.rs

@@ -40,7 +40,7 @@ impl Command for SubCommand {
         if matches!(input, PipelineData::Empty) {
             return Err(ShellError::PipelineEmpty { dst_span: head });
         }
-        input.map(move |value| helper(value, head), engine_state.ctrlc.clone())
+        input.map(move |value| helper(value, head), engine_state.signals())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/date/to_table.rs

@@ -40,7 +40,7 @@ impl Command for SubCommand {
         if matches!(input, PipelineData::Empty) {
             return Err(ShellError::PipelineEmpty { dst_span: head });
         }
-        input.map(move |value| helper(value, head), engine_state.ctrlc.clone())
+        input.map(move |value| helper(value, head), engine_state.signals())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/date/to_timezone.rs

@@ -55,7 +55,7 @@ impl Command for SubCommand {
         }
         input.map(
             move |value| helper(value, head, &timezone),
-            engine_state.ctrlc.clone(),
+            engine_state.signals(),
         )
     }