Wrap all/1 returns with an ok-tuple

[joeljuca]

SwissSchema's all/1 should be returning lists wrapped in ok-tuples:

# Today, all/1 returns a raw list:
User.all() # => [%User{}, %User{}, %User{}, ...]

# It should, instead:
User.all() # => {:ok, [%User{}, %User{}, %User{}, ...]}

The reason is simple: it's an IO op, which might fail due to reasons (network failure, db perms, schema mismatch, etc.). I know it differs from Ecto's default behavior, but I think we might improve the DX by standardizing the returned structure of this function.

Also, if Ecto's all/2 throws errors when things go wrong, we should be rescuing them to returning error-tupled values:

# Something is wrong – eg.: network is unavailable
User.all() # => {:error, %SomeError{}}

[joeljuca]

And now I'm wondering: should we have an equivalent bang function all!/1? 🤔