feat: make SigAction repr(transparent)&From<raw>&Into<raw> (#2326)

* feat: make SigAction repr(transparent)&From<raw>&Into<raw>

* style: fix clippy

changelog/2326.added.md

@@ -0,0 +1 @@
+make SigAction repr(transparent) & can be converted to/from the libc raw type

src/sys/signal.rs

@@ -753,11 +753,25 @@ pub enum SigHandler {
 }
 
 /// Action to take on receipt of a signal. Corresponds to `sigaction`.
+#[repr(transparent)]
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
 pub struct SigAction {
     sigaction: libc::sigaction
 }
 
+impl From<libc::sigaction> for SigAction {
+    fn from(value: libc::sigaction) -> Self {
+        Self {
+            sigaction: value
+        }
+    }
+}
+impl From<SigAction> for libc::sigaction {
+    fn from(value: SigAction) -> libc::sigaction {
+        value.sigaction
+    }
+}
+
 impl SigAction {
     /// Creates a new action.
     ///