add fail-fast behavior for frames

[the-mikedavis]

changes some behavior of Mint.WebSocket.decode/2

• it may return error tuples as {:ok, websocket, [{:error, reason}]} for fully contained bu invalid frames, such as text frames that are UTF-8
  • this fixes some of the non-strict test cases
• frames are now no longer returned frome decode/2 in shorthand format

connects #6

[the-mikedavis]

specifically this PR fixed the non-strict conformance for cases

• 3.2
• 3.3
• 4.1.3
• 4.1.4
• 4.2.3
• 4.2.4
• 5.15

but left 6.4.x cases as non-strict