Put CSV import function under its own module

src/invidious/user/imports.cr

@@ -1,6 +1,11 @@
 require "csv"
 
-def parse_subscription_export_csv(csv_content : String)
+struct Invidious::User
+  module Import
+    extend self
+
+    # Parse a youtube CSV subscription file
+    def parse_subscription_export_csv(csv_content : String)
       rows = CSV.new(csv_content, headers: true)
       subscriptions = Array(String).new
 
@@ -19,9 +24,10 @@ def parse_subscription_export_csv(csv_content : String)
         channel_id = row[0].strip
 
         next if channel_id.empty?
-
         subscriptions << channel_id
       end
 
       return subscriptions
+    end
+  end
 end