Workflow: Serve Method & Example Project

[CahidArda]

This PR contains changes made to add a Nextjs example project for Qstash Workflows.

Here is the list of major changes made:

• Made steps abort (throw error) and stop execution once a step executes. This was needed in cases where the result of one step was being used for branching

  const result = context.run(...)
  // throws reading success from undefined error:
  if (result.success) {...}

• removed workflow.ts and its unittests. Instead, split the code into the context.ts and executor.ts files to simplify the project
• Added BaseLazyStep to make the auto executor agnostic with regards to the kind of step being run (sleep/sleepUntil/run). This simplified the code, made it possible to run sleep/sleepUntil parallel with run. Additionally, it will make adding future steps easier.
• Added import paths for @upstash/qstash/workflow and @upstash/qstash/workflow/nextjs

[linear[bot]]

DX-999 QStash workflow - feedback / sdk design