* Rename Header to AuraHeader
This prevents some type conflicts with the PolkadotJS Apps types.
* Fix test and benchmark builds
* Update AuraHeader in types.json
* runtime benchmarks: start
* merge tests + benchmarks infrastructure
* fix compilation
* Fix compilation issues with runtime-benchmark feature flag
Mainly involved pulling in correct dependencies and adding some functions
which were called but didn't yet exist.
* Fix broken compilation for tests
* Move header signing methods into trait
* Move signing related test helpers to own module
* Remove comment about feature flag
* Add constants to tests
* Add top level comment for testing utilities
Co-authored-by: Hernando Castano <castano.ha@gmail.com>