Fix | Rewinds the body if it is seekable

[Sammyjo20]

This PR fixes an issue where if you called a body method on a response and then used a different one after, it would be an empty string. This was because the body() method wasn't rewinding the underlying stream.

This PR fixes this issue.

[what-the-diff]

PR Summary 🚀

• Stream rewind after reading in body method 🔄
  The body method now rewinds the stream back to the start after reading it, ensuring no issues when reusing the stream.

• New dtoOrFail() method added 💥
  A helpful dtoOrFail() method has been introduced, which throws a LogicException if the response fails instead of just returning null.

• SaloonResponseTest improvements ✅
  The SaloonResponseTest now checks that json(), object(), and xml() methods all return the expected results, while also rewinding the stream back to its original position for smooth, worry-free operation! 😄

[Sammyjo20]

Self review