packet: Use Bytes instead of an array in Packet

The reason behind the switch is that `Packet` gets cloned in multiple
places. `Bytes` provides a zero-copy abstraction, where calling
`clone()` doesn't make an actual copy of the underlying data and all
instances point to the same memory.

However, the old layout containing a sized array is convenient for CUDA.
To not break CUDA support, this change introduces a new struct called
`PacketArray`, which a `Packet` can be converted into just before
calling GPU-based sigverify. That requires a copy, ideally just one.

At the same time, CPU-based sigverify and all the other components are
going to benefit from zero-copy properties of `Bytes`.

Author: vadorovsky

Cargo.lock

@@ -140,6 +140,7 @@ bs58 = { version = "0.5.1", default-features = false }
 bv = "0.11.1"
 bytemuck = "1.21.0"
 bytemuck_derive = "1.8.1"
+bytes = { version = "1.10", features = ["serde"] }
 cfg_eval = "0.1.2"
 chrono = { version = "0.4.39", default-features = false }
 console = "0.15.10"

Cargo.toml

@@ -11,6 +11,7 @@ edition = { workspace = true }
 
 [dependencies]
 bs58 = { workspace = true, features = ["alloc"] }
+bytes = { workspace = true, optional = true }
 bv = { workspace = true, features = ["serde"] }
 log = { workspace = true, features = ["std"] }
 serde = { workspace = true, features = ["rc"] }
@@ -34,7 +35,7 @@ serde_with = { workspace = true, features = ["macros"] }
 default = []
 # activate the frozen-abi feature when we actually want to do frozen-abi testing,
 # otherwise leave it off because it requires nightly Rust
-frozen-abi = []
+frozen-abi = ["bytes"]
 
 [lints]
 workspace = true

frozen-abi/Cargo.toml

@@ -1,5 +1,6 @@
 use {
     crate::abi_digester::{AbiDigester, DigestError, DigestResult},
+    bytes::Bytes,
     log::*,
     serde::Serialize,
     std::any::type_name,
@@ -507,6 +508,12 @@ impl AbiExample for IpAddr {
     }
 }
 
+impl AbiExample for Bytes {
+    fn example() -> Self {
+        Bytes::new()
+    }
+}
+
 // This is a control flow indirection needed for digesting all variants of an enum.
 //
 // All of types (including non-enums) will be processed by this trait, albeit the

frozen-abi/src/abi_example.rs

@@ -12,6 +12,7 @@ edition = { workspace = true }
 [dependencies]
 bincode = { workspace = true, optional = true }
 bitflags = { workspace = true }
+bytes = { workspace = true }
 cfg_eval = { workspace = true, optional = true }
 serde = { workspace = true, optional = true }
 serde_derive = { workspace = true, optional = true }