fix: Settings stores the URL on screen when another page stored a different one (closes #688)

The RPC and Blockscout "Save" buttons in Settings now set the URL in the stored record, inside the save. The save writes only the fields that differ from what the page last saved. Before this change, a "Save" of the URL that this page loaded kept another page's different URL stored. Before this change, the flash message for that save read "Saved.". A save refused because the network changed still stores nothing.

Model: opus-5-5

tests/settingsEndpointSave.test.js

@@ -28,7 +28,7 @@ test.each([
         const page = await bootPopup(unversionedValidProfile());
         await page.click("btn-settings");
         const url = page.value(input);
-        // The browser is not made to tell this page of the other page's write.
+        // This write sends this page no storage change event.
         page.storage.write("autistmask", {
             ...page.storage.read("autistmask"),
             [field]: "https://other-page.example.invalid",