Make protocol errors pretty

[davydog187]

A common complaint I hear from people is that error messages in Elixir are not pretty. Generally, this seems to be only the case when there are large structs in codebases that render in one line and are hard to read.

This PR changes the behavior to pretty inspect the structs in the case that a protocol is not implemented for some value.

The downside here is that the logging will no longer be in one line, but I think this is a fair tradeoff for legibility

Before

** (Protocol.UndefinedError) protocol String.Chars not implemented for %Foo{a: %Foo{a: nil, b: nil, c: nil, d: nil}, b: %Foo{a: nil, b: nil, c: nil, d: nil}, c: %Foo{a: nil, b: nil, c: nil, d: nil}, d: %Foo{a: nil, b: nil, c: nil, d: nil}} of type Foo (a struct)
    (elixir 1.18.0-dev) lib/string/chars.ex:3: String.Chars.impl_for!/1
    (elixir 1.18.0-dev) lib/string/chars.ex:22: String.Chars.to_string/1
    iex:2: (file)

After

** (Protocol.UndefinedError) protocol String.Chars not implemented for type Foo (a struct)

Got value:

    %Foo{
      a: %Foo{a: nil, b: nil, c: nil, d: nil},
      b: %Foo{a: nil, b: nil, c: nil, d: nil},
      c: %Foo{a: nil, b: nil, c: nil, d: nil},
      d: %Foo{a: nil, b: nil, c: nil, d: nil}
    }

    (elixir 1.18.0-dev) lib/string/chars.ex:3: String.Chars.impl_for!/1
    (elixir 1.18.0-dev) lib/string/chars.ex:22: String.Chars.to_string/1
    iex:2: (file)

[josevalim]

Thank you! Can you please double check CI? I assume the tests need updating too!

[davydog187]

Thanks @josevalim! tests have been fixed locally, and I changed the formatting to indent it a bit. Please run the CI and take a look :)

[josevalim]

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