feat: kernel memory plugin + unified source menu + driver improvements

- KernelMemory plugin: kernel-mode process/physical memory R/W via IOCTL driver
- rcxdrv.sys: MmCopyMemory for reads, MDL mapping with correct cache types
  (MmCached for RAM, MmNonCached for MMIO only — fixes cache corruption BSOD)
- Driver reconnect: ensureDriverLoaded tries device handle first, no auto
  stop+delete cycle. Manual unload closes handle only, service stays running.
- Unified source menu: ProviderRegistry::populateSourceMenu() shared by both
  main window Data Source menu and RcxEditor inline picker (icons + dll names)
- IProviderPlugin::populatePluginMenu() for conditional plugin actions
  (e.g. "Unload Kernel Driver" only when loaded)
- Physical memory mode removed from selectTarget (access via context menu only)
- requestOpenProviderTab sets base address from provider after template load
- Address parser: vtop(), cr3(), physRead() callbacks for kernel paging expressions

src/iplugin.h

@@ -10,8 +10,9 @@
     #define RCX_PLUGIN_EXPORT __attribute__((visibility("default")))
 #endif
 
-// Forward declaration
+// Forward declarations
 namespace rcx { class Provider; }
+class QMenu;
 
 /**
  * Plugin interface for Reclass
@@ -129,6 +130,13 @@ public:
      * @return true if enumerateProcesses() should be called
      */
     virtual bool providesProcessList() const { return false; }
+
+    /**
+     * Add plugin-specific actions to the source menu (optional).
+     * Called each time the source menu is shown. Only add items when relevant
+     * (e.g., "Unload Driver" only when the driver is loaded).
+     */
+    virtual void populatePluginMenu(QMenu*) {}
 };
 
 // Plugin factory function signature