babe: report equivocations (#6362)

* slots: create primitives crate for consensus slots

* offences: add method to check if an offence is unknown

* babe: initial equivocation reporting implementation

* babe: organize imports

* babe: working equivocation reporting

* babe: add slot number to equivocation proof

* session: move duplicate traits to session primitives

* babe: move equivocation stuff to its own file

* offences: fix test

* session: don't have primitives depend on frame_support

* babe: use opaque type for key owner proof

* babe: cleanup client equivocation reporting

* babe: cleanup equivocation code in pallet

* babe: allow sending signed equivocation reports

* node: fix compilation

* fix test compilation

* babe: return bool on check_equivocation_proof

* babe: add test for equivocation reporting

* babe: add more tests

* babe: add test for validate unsigned

* babe: take slot number in generate_key_ownership_proof API

* babe: add benchmark for equivocation proof checking

* session: add benchmark for membership proof checking

* offences: fix babe benchmark

* babe: add weights based on benchmark results

* babe: adjust weights after benchmarking on reference hardware

* babe: reorder checks in check_and_report_equivocation

substrate/primitives/core/src/lib.rs

@@ -333,6 +333,11 @@ pub fn to_substrate_wasm_fn_return_value(value: &impl Encode) -> u64 {
 	res
 }
 
+/// The void type - it cannot exist.
+// Oh rust, you crack me up...
+#[derive(Clone, Decode, Encode, Eq, PartialEq, RuntimeDebug)]
+pub enum Void {}
+
 /// Macro for creating `Maybe*` marker traits.
 ///
 /// Such a maybe-marker trait requires the given bound when `feature = std` and doesn't require