discordid: remove all ID-related casts

In the same vein as mautrix-whatsapp, -slack and others, do not make
assumptions about how the ID is represented in the connector code. Let
the discordid package be entirely responsible.

pkg/connector/login_generic.go

@@ -24,7 +24,6 @@ import (
 	"github.com/rs/zerolog"
 	"maunium.net/go/mautrix/bridgev2"
 	"maunium.net/go/mautrix/bridgev2/database"
-	"maunium.net/go/mautrix/bridgev2/networkid"
 
 	"go.mau.fi/mautrix-discord/pkg/discordid"
 )
@@ -71,7 +70,7 @@ func (dl *DiscordGenericLogin) FinalizeCreatingLogin(ctx context.Context, token
 
 	dl.Session = session
 	ul, err := dl.User.NewLogin(ctx, &database.UserLogin{
-		ID: networkid.UserLoginID(user.ID),
+		ID: discordid.MakeUserLoginID(user.ID),
 		Metadata: &discordid.UserLoginMetadata{
 			Token:            token,
 			HeartbeatSession: session.HeartbeatSession,