hypervisor: reevaluate #[allow] attributes

Remove stale #[allow]s whose lints no longer fire, convert the
unconditionally-firing ones to #[expect], and keep the conditional
ones as #[allow] (e.g. large_enum_variant only fires when both kvm
and mshv are enabled; a nonminimal_bool only on x86). The many
unreachable_patterns allows are feature-gated and left as #[allow].

Part of #8326.

Signed-off-by: Tushar Khatri <hello@tusharkhatri.in>

hypervisor/src/kvm/mod.rs

@@ -1512,7 +1512,7 @@ pub type KvmResult<T> = result::Result<T, KvmError>;
 
 impl KvmHypervisor {
     /// Create a hypervisor based on Kvm
-    #[allow(clippy::new_ret_no_self)]
+    #[expect(clippy::new_ret_no_self)]
     pub fn new() -> hypervisor::Result<Arc<dyn hypervisor::Hypervisor>> {
         let kvm_obj = Kvm::new().map_err(|e| hypervisor::HypervisorError::VmCreate(e.into()))?;
         let api_version = kvm_obj.get_api_version();