Improved dump for calls and responses, particularly for chaining

[willbakst]

Description

• The original implementation of dump only included a few fields, there are many more we should consider.
• We should look into improving dump for chained prompts so that a single dump will show the entire trace information.

[willbakst]

With the new interface, an idea here would be to enable making a computed field any object with a str method (which should already be the case). This would mean you could compute the field as an e.g. OpenAICallResponse and still get it in the dump but properly template it as just the string content.