This introduces a `Pender` struct with enum cases for thread-mode, interrupt-mode and
custom callback executors. This avoids calls through function pointers when using only
the thread or interrupt executors. Faster, and friendlier to `cargo-call-stack`.
`embassy-executor` now has `arch-xxx` Cargo features to select the arch and to enable
the builtin executors (thread and interrupt).
This commit provides a method to verify that firmware has been signed with a private key given its public key. The implementation uses ed25519-dalek as the signature verifier. An "ed25519" feature is required to enable the functionality. When disabled (the default), calling the firmware updater's verify method will return a failure.
* Add nRF91 as target in CI builds
* Add example linker scripts for nrf91
* Make less nRF52 assumptions example config
* Add llvm-tools-preview required for cargo objcopy example
