Extract transaction types into a crate

[dannywillems]

We might want to provide the structures to external projects llike the multisig implementation.

The project mina-multi-sig does copy some structures from o1js and mina-rust to implement multisig for zkApp transaction.

Extracting the transaction structures from the crate mina-tree/ledger would also make the code clearer.

It would be useful in particular to @jCabala and @scaraven.

The different transaction types can be found here

Requirements

• The crate must be no_std compatible to support embedded/constrained environments (e.g., hardware wallets, WASM)
• Each field must be documented with rustdoc comments explaining its purpose and semantics

Documentation requirements

• The documentation for the new crate should include a TODO reference to Add documentation on zkApp transaction signing #1748 (zkApp transaction signing documentation). The signing documentation in Add documentation on zkApp transaction signing #1748 will depend on the types defined in this crate.
• Reference the zkApp signing RFC: https://mina-rust.o1labs.org/researchers/zkapp-signing (once published)
• Once the crate is published, update the zkApp signing RFC to link back to the crate documentation

[dannywillems]

Assigned to @richardpringle as part of the ledger crate exploration.