🐛 Comparing stream to itself returns false

[pleonex]

DataStream.Compare with the same object was returning that the stream was not identical. We were not detecting that it's the same instance and trying to read twice from the same object.

This PR closes #189

Quality check list

• Related code has been tested automatically or manually
• Related documentation is updated
• I acknowledge I have read and filled this checklist and accept the
  developer certificate of origin

Acceptance criteria

• Compare method to itself returns true

Follow-up work

None

Example

using var stream1 = new DataStream();
stream1.WriteByte(0xCA);
DataStream stream2 = stream1;
Assert.IsTrue(stream1.Compare(stream2))