pv: Improve API by marking some functions as must_use

Make the API less prone to error by specifying some of them as must_use.
This avoids issues that the result is not used.

Signed-off-by: Marc Hartmayer <marc@linux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>

rust/pv/src/crypto.rs

@@ -119,6 +119,7 @@ impl SymKeyType {
     }
 
     /// Returns true if the [`SymKeyType`] is an AEAD key
+    #[must_use]
     pub const fn is_aead(&self) -> bool {
         self.tag_len().is_some()
     }

rust/pv/src/req/keyslot.rs

@@ -182,6 +182,7 @@ impl Keyslot {
     }
 
     /// Return the public host key hash size for the given version of the key-slot in bytes
+    #[must_use]
     pub fn phkh_size(&self) -> u32 {
         match self {
             Keyslot::V1(_) => KeyslotV1::PHKH_SIZE,
@@ -190,6 +191,7 @@ impl Keyslot {
     }
 
     /// Return the size of the key-slot in bytes
+    #[must_use]
     pub fn size(&self) -> usize {
         match self {
             Keyslot::V1(_) => KeyslotV1::SIZE,