[playground] accumulate errors while parsing span attributes for prompt playground

[Parker-Stafford]

Accumulate errors while trying to parse span attributes to pre-populate the playground for span replay.

Attempt to parse span attributes starting with the most important and most strict parsing, accumulating any errors and falling back to less strict parsing.

Things to parse and order of priority:

• inputs
  • input_messages (single part content)
  • input.value
• outputs
  • output_messages (single part)
  • output.value
• invocation parameters
• prompt template variables
• tools

[Parker-Stafford]

completed in #4941