Generate code evaluators

[ianarawjo]

• Adds a purple GenAI button to Code Evaluator Nodes, to allow easier creation of evaluation functions. (NOTE: This, like the TextFields and Items Nodes GenAI features, is experimental and requires an OpenAI API key to access.)
• Adds a drop-down to LLM evaluators
• Ensures LLM evaluators load cache'd responses on load
• Fixes a bug where right-clicking in pop-up Inspectors would bring up the node context menu.
• Internally, refactors evaluator nodes to have inner components that take care of running evaluations, in preparation for multi-eval and running evals elsewhere

This rolls in changes from the ongoing multi-eval branch, which have been sitting in the branch since New Years.