Force enumeration of global collections before using them (#106)

This PR closes #105 

This PR fixes exceptions caused by changing a collection's contents
while it is being enumerated. This can often happen with Guild- and
MemberDatas. By using `ToArray()` on these global collections and using
it in the `foreach` loop, we create a new copy of the collection,
preventing any modification to it.

While this does introduce a lot of memory allocations, there is no
fixing that. Usually, the fix to these exceptions would be to convert
the `foreach` to a reverse-`for`. However, because indices cannot be
used on these collections, that is not possible.

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

src/Services/Update/MemberUpdateService.cs

@@ -63,7 +63,8 @@ public sealed partial class MemberUpdateService : BackgroundService
         var guildData = await _guildData.GetData(guildId, ct);
         var defaultRole = GuildSettings.DefaultRole.Get(guildData.Settings);
         var failedResults = new List<Result>();
-        foreach (var data in guildData.MemberData.Values)
+        var memberDatas = guildData.MemberData.Values.ToArray();
+        foreach (var data in memberDatas)
         {
             var tickResult = await TickMemberDataAsync(guildId, guildData, defaultRole, data, ct);
             failedResults.AddIfFailed(tickResult);