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/mshv/mod.rs

@@ -233,7 +233,7 @@ pub struct MshvHypervisor {
 
 impl MshvHypervisor {
     /// Create a hypervisor based on Mshv
-    #[allow(clippy::new_ret_no_self)]
+    #[expect(clippy::new_ret_no_self)]
     pub fn new() -> hypervisor::Result<Arc<dyn hypervisor::Hypervisor>> {
         let mshv_obj =
             Mshv::new().map_err(|e| hypervisor::HypervisorError::HypervisorCreate(e.into()))?;
@@ -586,7 +586,7 @@ impl cpu::Vcpu for MshvVcpu {
         Ok(())
     }
 
-    #[allow(non_upper_case_globals)]
+    #[expect(non_upper_case_globals)]
     fn run(&mut self) -> std::result::Result<cpu::VmExit, cpu::HypervisorCpuError> {
         match self.fd.run() {
             Ok(x) => match x.header.message_type {

hypervisor/src/mshv/x86_64/emulator.rs

@@ -23,7 +23,7 @@ pub struct MshvEmulatorContext<'a> {
 
 impl MshvEmulatorContext<'_> {
     // Do the actual gva -> gpa translation
-    #[allow(non_upper_case_globals)]
+    #[expect(non_upper_case_globals)]
     fn translate(&self, gva: u64, flags: u32) -> Result<u64, PlatformError> {
         if let Some((cached_gva, cached_gpa)) = self.mapping
             && cached_gva == gva