Convert all boards to new syntax

[dglazkov]

A checklist of the boards that we want to convert:

• accumulating-context.ts
• board-as-function.ts
• board-caller.ts
• gemini-generator.ts
• gemini-pro-vision.ts
• math-chain.ts
• math-imperative.ts
• math.ts
• mock-text-generator.ts
• openai-gpt-35-turbo.ts
• openai-gpt-4-vision.ts
• search-summarize-as-recipe.ts
• search-summarize.ts
• simplest.ts
• text-generator-recipe.ts
• text-generator.ts
• tour-guide-writer.ts

Boards we don't need to convert, since they are WIP or obsolete:

• healer.ts
• json-generator.ts
• json-validator.ts
• list-files.ts
• retry.ts