Get the testing cfg to transfer from top level app to alohomora, so that testing features and APIs are conditionally present

[KinanBab]

e.g. TestContext, discard_box, #[derive(Debug)], etc

[KinanBab]

Plan:

• Create a new feature in Alohomora to signify test: e.g. testing or something similar, or maybe test if it does not conflict with the builtin test config
• Use https://stackoverflow.com/questions/68618789/is-it-possible-to-enable-a-rust-feature-only-in-test in apps to specify that alohomora should get testing feature in tests. Alternatively, investigate some build.rs shenanigans.
• TestContext, TestPolicy, etc just dissappear, instead their content is added as conditional impl blocks to Context, Policy, etc