fix: prevent GPU-not-found crash when switching to hybrid mode

Two related bugs caused envycontrol to crash with 'Could not find Nvidia
GPU' even when switching to a mode that doesn't need the GPU visible:

1. get_current_mode() required BOTH the blacklist file AND the udev
   removal rule to report 'integrated'.  If only the udev rule existed
   (e.g. after a partial or interrupted previous switch), the function
   returned 'hybrid', misleading the CachedConfig adapter.

   Fix: any single EnvyControl-specific integrated-mode file is now
   sufficient to report integrated mode, since all three paths
   (/etc/modprobe.d/blacklist-nvidia.conf,
    /etc/udev/rules.d/50-remove-nvidia.rules,
    /lib/udev/rules.d/50-remove-nvidia.rules)
   are written exclusively by envycontrol for that mode.

2. CachedConfig.adapter() called create_cache_file() whenever the
   current mode was detected as hybrid, including when the requested
   switch target was also hybrid.  create_cache_file() calls
   get_nvidia_gpu_pci_bus() which parses lspci output; if a stale udev
   removal rule was hiding the NVIDIA device the function called
   sys.exit(1), aborting before cleanup() ever ran.

   Fix: skip cache creation when the target switch is 'hybrid', since
   hybrid mode never consumes the cached PCI bus value.

Author: vjaykrsna

envycontrol.py

@@ -647,7 +647,11 @@ def adapter(self):
         global get_nvidia_gpu_pci_bus
         use_cache = os.path.exists(CACHE_FILE_PATH)
 
-        if self.is_hybrid():  # recreate cache file when in hybrid mode
+        # Only cache the GPU PCI bus when leaving hybrid mode.
+        # Switching *to* hybrid never needs the cached value and the GPU
+        # may not be visible via lspci if old udev removal rules are still
+        # in place, which would make create_cache_file() exit early.
+        if self.is_hybrid() and self.app_args.switch != 'hybrid':
             self.create_cache_file()
 
         if use_cache:
@@ -717,7 +721,9 @@ def write_cache_file(self):
 
 def get_current_mode():
     mode = 'hybrid'
-    if os.path.exists(BLACKLIST_PATH) and (os.path.exists(UDEV_INTEGRATED_PATH) or os.path.exists('/lib/udev/rules.d/50-remove-nvidia.rules')):
+    if (os.path.exists(BLACKLIST_PATH) or
+            os.path.exists(UDEV_INTEGRATED_PATH) or
+            os.path.exists('/lib/udev/rules.d/50-remove-nvidia.rules')):
         mode = 'integrated'
     elif os.path.exists(XORG_PATH) and os.path.exists(MODESET_PATH):
         mode = 'nvidia'