feat: add implicit conversion on gitlabcollectionresponse<T>

[Toa741]

• With .Net 10 and the new AsyncEnumerable (that was before in System.Linq.Async), it seems that on Linq methods (Where, Select, ...), it might not know which method to take (Select(IEnumerable<>) or Select(IAsyncEnumerable<>)
• Adding 2 methods to implicitly convert the Collection

While digging a bit:

• AsEnumerable() exists in System.Linq.Enumerable and should be fully equivalent (no cost, implicit conversion). Might not be needed to add this one explicitely
• ToAsyncEnumerable() exists in System.Linq.AsyncEnumerable, but is made for converting a IEnumerable to a IAsyncEnumerable (involves additional operations like iterating on the collection)