Add helper method to check whether ctrl+c was pressed, adopt it (#7482)

I've been working on streaming and pipeline interruption lately. It was
bothering me that checking ctrl+c (something we want to do often) always
requires a bunch of boilerplate like:
```rust
use std::sync::atomic::Ordering;

if let Some(ctrlc) = &engine_state.ctrlc {
     if ctrlc.load(Ordering::SeqCst) {
          ...
```
I added a helper method to cut that down to:

```rust
if nu_utils::ctrl_c::was_pressed(&engine_state.ctrlc) {
    ...
```

crates/nu-engine/src/eval.rs

@@ -31,10 +31,8 @@ pub fn eval_call(
     call: &Call,
     input: PipelineData,
 ) -> Result<PipelineData, ShellError> {
-    if let Some(ctrlc) = &engine_state.ctrlc {
-        if ctrlc.load(core::sync::atomic::Ordering::SeqCst) {
-            return Ok(Value::Nothing { span: call.head }.into_pipeline_data());
-        }
+    if nu_utils::ctrl_c::was_pressed(&engine_state.ctrlc) {
+        return Ok(Value::Nothing { span: call.head }.into_pipeline_data());
     }
     let decl = engine_state.get_decl(call.decl_id);