Add support for parallel streaming of responses

[denk0403]

• Stream test execution output as JSON lines.
  • Ensure memory usage remains low.
• Increase max step count.
• Investigate parallelizing test execution.
  • Goroutines and Channels?
  • sync.WaitGroup{}

Goal

Support executing the following machine:

start: a
accept: accept
reject: reject

transitions:
- [a, _, b, 1, R]
- [b, _, c, 1, R]
- [c, _, d, 1, R]
- [d, _, a, 1, L]
- [e, _, accept, 1, R]
- [a, 1, c, 1, L]
- [b, 1, b, 1, R]
- [c, 1, e, _, L]
- [d, 1, d, 1, L]
- [e, 1, a, _, L]

Current behavior:

Error: This test took too long or encountered an infinite loop.
Skipping this test.