Errors and inconsistencies in examples

[gbryant-arm]

Describe the bug

• examples/rust-examples/audio-event-triangulation doesn't compile
• A bunch of examples never get built. The following examples aren't picked up by workspaces/shared.mk:

  audio-event-triangulation
  darknet-inference-native (not merged yet)
  file-seek
  huffman-encoding
  image-processing
  logistic-regression
  nop
  prime-numbers-generator
  random-source
  string-search
  tflite-inference-native-mnist (not merged yet)
  

• Some examples have no Makefile specifying the target (wasm32-wasi)
• Many crates under examples/ are buried in directories with no Cargo.toml, making them impossible to be scanned by tools like rust-analyzer. NB: This is also an issue for sdk/
• In light of Add VOD deployment job to GitHub workflows #597, we should wonder whether it makes sense to compile and run these examples in CI

To Reproduce
Check out examples/