WASHINGTON — The fertile mind of Justice Stephen Breyer has conjured a stream of hypothetical questions through the years that have, in the words of a colleague, “befuddled” lawyers and justices alike.Breyer, 83, seemed a bit subdued as he sat through the last of more than 2,000 arguments Wednesday in which he has taken part during 28 years on the high court. His wife, Joanna, also was in the courtroom.But at the end of the case about Oklahoma’s authority to prosecute people accused of crimes on …