Show path for schema errors

[sporto]

I tried decoding our schema.

And it fails with an error like

Error(UnexpectedFormat([DecodeError(expected: "another type", found: "Object", path: ["schemas",  "values"])]))

This is comming from the dictionary decoder, which doesn't give enough information about the value that is failing.

Our schema fails because some schema are missing the type property.
It is quite hard to figure out where as it is quite large.

This is an attempt at providing more information (they key of the dictionary that fails):

Error(UnexpectedFormat([DecodeError(expected: "another type", found: "Object", path: ["schemas",  "thing"])]))

[CrowdHailer]

Should we make the suggestion that this is how dynamic.dict should work anyway?
I see the benefit and I like the test coverage, but I'm slight reluctant to support this patch to decoding.

[sporto]

I agree that the dynamic dict decoder should do something like this. I will look into it.
But that could take a while. In the meantime it would be great to have something here that can show an informative error.

[sporto]

Looking at std https://github.com/gleam-lang/stdlib/blob/main/src/gleam/dynamic.gleam#L968
It seems it will be much simpler to show the informative error there. So let's hold on this PR.

[sporto]

gleam-lang/stdlib#741

This will show values[index].
Not really possible to show the key name in the standard lib I think.

But we could do better here by showing the key name. As the key is a string.

[CrowdHailer]

alight lets go for it. thanks for the investigation