refactor: Apply Result pattern to avoid returning null in private methods

[MrDave1999]

This pattern has been applied for two reasons:

• It makes the producer code more expressive because it uses factory methods such as Success and Failure instead of returning a null value.
• It makes the consumer code more expressive because it uses properties such as IsSuccess and IsFailed instead of performing a null check.

Expressive code means that it indicates its own intention so that it is clear at first glance.

Performance

Performance will not be affected because the "ref struct" type is used.
See https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/ref-struct

You can use the ref modifier in the declaration of a structure type. Instances of a ref struct type are allocated on the stack and can't escape to the managed heap.

This means that there will be no load on the garbage collector, reducing the memory reallocations on the heap.