add test suite

[tjjfvi]

• added a test suite that automatically tests every HVM file in examples/ and tests/programs/ across all enabled runtimes
• added a CI workflow to build & test every push to a PR
• adjusted all of the examples/ programs to run in a reasonable amount of time by default
• fixed several bugs uncovered in testing:
  • fixed C/CUDA implementation of I24
  • fixed a bug with new_f24 that "rounded" some NaN patterns to 0
  • fixed C/CUDA readback of large numbers like 16777215 (which were being printed as random characters instead)

[VictorTaelin]

Seems like this doesn't test the compiled versions yet, right? It should be good to add that later, as the compiled functions are a major source of bugs.