redox-driver-core: add PciErsResult — Linux pci_ers_result 6-state enum

Mirrors Linux 7.1's pci_ers_result (include/linux/pci.h:920-938):
None/CanRecover/NeedReset/Disconnect/Recovered/NoAerDriver. This is
the vocabulary Driver::error_detected will return when the AER
recovery flow is wired to bound drivers. Currently the legacy
RecoveryAction enum (Handled/ResetDevice/RescanBus/Fatal) coexists
for the existing on_error callback — PciErsResult is the richer model
that will replace it once the driver-manager → driver IPC channel
exists for AER dispatch.

local/recipes/drivers/redox-driver-core/source/src/driver.rs

@@ -61,6 +61,26 @@ pub enum RecoveryAction {
     Fatal,
 }
 
+/// The 6-state PCI error-recovery result, mirroring Linux's
+/// `pci_ers_result` (include/linux/pci.h:920-938). Used by
+/// `Driver::error_detected` to report whether the driver can recover,
+/// needs a reset, or is dead.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum PciErsResult {
+    /// No action taken.
+    None,
+    /// Driver can recover without a device reset.
+    CanRecover,
+    /// Driver requests a slot reset before continuing.
+    NeedReset,
+    /// Device is permanently lost; disconnect.
+    Disconnect,
+    /// Recovery completed successfully.
+    Recovered,
+    /// No AER-capable driver is bound.
+    NoAerDriver,
+}
+
 /// A device driver that can bind to and manage devices.
 pub trait Driver: Send + Sync {
     /// Returns the unique driver name, such as `"nvmed"` or `"e1000d"`.