Add mina-tx-type crate with zkApp transaction types

Create a new standalone crate `mina-tx-type` that extracts transaction type
structures from the ledger crate. This enables external projects to reuse
these structures without duplicating code.

The crate includes:
- ZkAppCommand and related types (FeePayer, AccountUpdate, CallForest)
- Account update body with all fields (update, balance_change, preconditions)
- Preconditions (network, account, valid_while)
- SetOrKeep and OrIgnore wrapper types
- Authorization types (AuthorizationKind, MayUseToken, Permissions)
- Primitive types (Fee, Amount, Balance, Nonce, Slot, etc.)

Key features:
- no_std only (no std feature) for embedded/constrained environments
- Comprehensive rustdoc documentation for all fields
- Generic over public key and field element types

References issue #1665.

Author: dannywillems

Cargo.lock

@@ -7,6 +7,7 @@ members = [
   "ledger",
   "macros",
   "mina-p2p-messages",
+  "mina-tx-type",
   "node",
   "node/account",
   "node/common",
@@ -147,6 +148,7 @@ mina-p2p-messages = { path = "mina-p2p-messages" }
 mina-poseidon = { git = "https://github.com/o1-labs/proof-systems", tag = "0.2.0" }
 mina-signer = { git = "https://github.com/o1-labs/proof-systems", tag = "0.2.0" }
 mina-transport = { path = "tools/transport" }
+mina-tx-type = { path = "mina-tx-type" }
 mio = { version = "1.0.4", features = ["os-poll", "net"] }
 multiaddr = "0.18.1"
 multihash = { version = "0.18.1", features = ["blake2b"] }

Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "mina-tx-type"
+version = "0.18.1"
+edition = "2021"
+description = "Transaction types for the Mina Protocol"
+license = "Apache-2.0"
+readme = "README.md"
+repository = "https://github.com/o1-labs/mina-rust"
+keywords = ["mina", "blockchain", "cryptocurrency", "zkapp", "transaction"]
+categories = ["cryptography::cryptocurrencies"]
+
+[dependencies]
+
+[dev-dependencies]

mina-tx-type/Cargo.toml

@@ -0,0 +1,46 @@
+//! Transaction types for the Mina Protocol
+//!
+//! This crate provides standalone data structures representing Mina Protocol
+//! transaction types. It is designed to be `no_std` compatible for use in
+//! constrained environments such as hardware wallets and WebAssembly.
+//!
+//! # Overview
+//!
+//! The Mina Protocol supports two primary user-initiated transaction types:
+//!
+//! - **Signed Commands**: Traditional payments and stake delegations authorized
+//!   by a cryptographic signature.
+//! - **zkApp Commands**: Complex multi-account operations using zero-knowledge
+//!   proofs for authorization and state updates.
+//!
+//! # zkApp Transaction Structure
+//!
+//! A zkApp command consists of:
+//! - A **fee payer** account that pays the transaction fee
+//! - A tree of **account updates** that modify account state
+//! - A **memo** field for user-defined metadata
+//!
+//! Each account update can specify:
+//! - State updates (app state, delegate, permissions, etc.)
+//! - Balance changes
+//! - Preconditions that must be satisfied
+//! - Authorization method (signature, proof, or none)
+//!
+//! # Documentation References
+//!
+//! For detailed information about zkApp transaction signing, see:
+//! - TODO: Issue #1748 - zkApp transaction signing documentation
+//! - <https://mina-rust.o1labs.org/researchers/zkapp-signing>
+//!
+//! # no_std Support
+//!
+//! This crate is `no_std` by design to support embedded and constrained
+//! environments such as hardware wallets and WebAssembly.
+
+#![no_std]
+
+extern crate alloc;
+
+pub mod zkapp;
+
+pub use zkapp::*;