[REPO] - Make hotshot_example a feature flag

[shenkeyao]

What is this task and why do we need to work on it?

Make hotshot_example a feature flag rather than a RUSTFLAG. Then we could create feature flags in downstream crates that enable this, like

[features]
testing = ["hotshot-testing/hotshot-example"]

What work will need to be done to complete this task?

No response

Are there any other details to include?

No response

What are the acceptance criteria to close this issue?

Code builds and is useable in the downstream crate.

Branch work will be merged to (if not the default branch)

No response