Fix nested list selection state in MudSelectExtended - #657

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/github-script@60a0d83039c74a4aee543508d2ffcb1c3799cdea, actions/setup-dotnet@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Dereference of a possibly null reference.

Nullability of reference types in type of parameter 'sender' of 'void MudWatch.Elapse(object sender, ElapsedEventArgs args)' doesn't match the target delegate 'ElapsedEventHandler' (possibly because of nullability attributes).

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Possible null reference argument for parameter 'arg' in 'ICollection<T?> Func<ICollection<T?>, ICollection<T?>>.Invoke(ICollection<T?> arg)'.

Possible null reference argument for parameter 'arg' in 'ICollection<T?> Func<ICollection<T?>, ICollection<T?>>.Invoke(ICollection<T?> arg)'.

Dereference of a possibly null reference.

Nullability of reference types in type of parameter 'sender' of 'void MudWatch.Elapse(object sender, ElapsedEventArgs args)' doesn't match the target delegate 'ElapsedEventHandler' (possibly because of nullability attributes).

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.