Redo primitives, abi

Consolidates all primitives into a single crate. We didn't benefit from its
fragmentation. I'm hesitant to say the new internal-organization is better (it
may be just as clunky), but it's at least in a single crate (not spread out
over micro-crates).

The ABI is the most distinct. We now entirely own it. Block header hashes don't
directly commit to any BABE data (avoiding potentially ~4 KB headers upon
session changes), and are hashed as borsh (a more widely used codec than
SCALE). There are still Substrate variants, using SCALE and with the BABE data,
but they're prunable from a protocol design perspective.

Defines a transaction as a Vec of Calls, allowing atomic operations.

substrate/primitives/src/instructions/out.rs

@@ -0,0 +1,21 @@
+use zeroize::Zeroize;
+
+use borsh::{BorshSerialize, BorshDeserialize};
+
+use crate::{address::ExternalAddress, balance::ExternalBalance};
+
+/// An instruction on how to transfer coins out.
+#[derive(Clone, PartialEq, Eq, Debug, Zeroize, BorshSerialize, BorshDeserialize)]
+pub enum OutInstruction {
+  /// Transfer to the specified address.
+  Transfer(ExternalAddress),
+}
+
+/// An instruction on how to transfer coins out with the balance to use for the transfer out.
+#[derive(Clone, PartialEq, Eq, Debug, Zeroize, BorshSerialize, BorshDeserialize)]
+pub struct OutInstructionWithBalance {
+  /// The instruction on how to transfer coins out.
+  pub instruction: OutInstruction,
+  /// The balance to use for the transfer out.
+  pub balance: ExternalBalance,
+}