Avoid OS specific function uname()

It is necessary when using the seedsigner-emulator project on Windows for example

src/seedsigner/models/settings.py

@@ -1,5 +1,6 @@
 import json
 import os
+import platform
 
 from typing import Any, List
 
@@ -10,7 +11,7 @@ from .singleton import Singleton
 
 
 class Settings(Singleton):
-    HOSTNAME = os.uname()[1]
+    HOSTNAME = platform.uname()[1]
     SEEDSIGNER_OS = "seedsigner-os"
     SETTINGS_FILENAME = "/mnt/microsd/settings.json" if HOSTNAME == SEEDSIGNER_OS else "settings.json"
         
@@ -202,4 +203,4 @@ class Settings(Singleton):
                 # set persistent settings to only have disabled as an option, adding additional help text that microSD is removed
                 entry = SettingsDefinition.get_settings_entry(SettingsConstants.SETTING__PERSISTENT_SETTINGS)
                 entry.selection_options = SettingsConstants.OPTIONS__ONLY_DISABLED
-                entry.help_text = "MicroSD card is removed"
+                entry.help_text = "MicroSD card is removed"