DbContexts aren't handled in a thread safe way

[gunnbr]

Gthx occasionally crashes with the following stack trace, apparently due to improper handling of DbContexts:

2025-12-08 02:07:06.613 +00:00 [Error] An exception occurred while iterating over the results of a query for context type '"GthxData.GthxDataContext"'."
""System.InvalidOperationException: A second operation was started on this context before a previous operation completed. This is usually caused by different threads concurrently using the same instance of DbContext. For more information on how to avoid threading issues with DbContext, see https://go.microsoft.com/fwlink/?linkid=2097913.
   at Microsoft.EntityFrameworkCore.Internal.ConcurrencyDetector.EnterCriticalSection()
   at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()"
System.InvalidOperationException: A second operation was started on this context before a previous operation completed. This is usually caused by different threads concurrently using the same instance of DbContext. For more information on how to avoid threading issues with DbContext, see https://go.microsoft.com/fwlink/?linkid=2097913.
   at Microsoft.EntityFrameworkCore.Internal.ConcurrencyDetector.EnterCriticalSection()
   at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()
   at System.Linq.Enumerable.TryGetSingle[TSource](IEnumerable`1 source, Boolean& found)
   at lambda_method57(Closure , QueryContext )
   at Gthx.Data.GthxSqlData.AddYoutubeTitle(String item, String title) in /source/Gthx.Data/Gthx.Data/GthxSqlData.cs:line 155
   at Gthx.Bot.Modules.YoutubeModule.GetAndSaveTitle(String url, String id, String channel, String user, Int32 referenceCount) in /source/Gthx.Bot/Modules/YoutubeModule.cs:line 70
2025-12-08 02:07:06.613 +00:00 [Error] YoutubeModule.GetAndSaveTitle failed!
System.InvalidOperationException: A second operation was started on this context before a previous operation completed. This is usually caused by different threads concurrently using the same instance of DbContext. For more information on how to avoid threading issues with DbContext, see https://go.microsoft.com/fwlink/?linkid=2097913.
   at Microsoft.EntityFrameworkCore.Internal.ConcurrencyDetector.EnterCriticalSection()
   at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()
   at System.Linq.Enumerable.TryGetSingle[TSource](IEnumerable`1 source, Boolean& found)
   at lambda_method57(Closure , QueryContext )
   at Gthx.Data.GthxSqlData.AddYoutubeTitle(String item, String title) in /source/Gthx.Data/Gthx.Data/GthxSqlData.cs:line 155
   at Gthx.Bot.Modules.YoutubeModule.GetAndSaveTitle(String url, String id, String channel, String user, Int32 referenceCount) in /source/Gthx.Bot/Modules/YoutubeModule.cs:line 70

This must be fixed to handle the DbContext properly.