radicle: add Op::load method — heartwood

Adds an Op::load helper method for loading an Entry, given its Oid and the store it is stored in.

This can be useful for downstream consumers to inspect operations on COBs given a single Oid, without having to load the entire object and/or graph.

It can also be useful when looking at implementing COB stream primitives.

 use serde::Serialize;
 use thiserror::Error;
 use radicle_cob as cob;
 use radicle_cob::history::{Entry, EntryId};
 use radicle_crypto::PublicKey;

     Git(#[from] git2::Error),
 }
 /// Error loading an `Op` from storage.
 #[derive(Error, Debug)]
 pub enum LoadError {
     #[error("failed to load Op at '{object}': {err}")]
     Load {
         object: git::Oid,
         #[source]
         err: Box<dyn std::error::Error + Send + Sync + 'static>,
     },
     #[error("failed to decode Op at '{object}': {err}")]
     Encoding {
         object: git::Oid,
         #[source]
         err: OpEncodingError,
     },
 }
 /// The `Op` is the operation that is applied onto a state to form a CRDT.
 ///
 /// Everything that can be done in the system is represented by an `Op`.

             Some(head) => repo.identity_doc_at(head).map(Some),
         }
     }
     /// Get the `Op` identified by the `id` in the provided `store`.
     pub fn load<S>(store: &S, id: git::Oid) -> Result<Self, LoadError>
     where
         S: cob::change::Storage<
             ObjectId = git::Oid,
             Parent = git::Oid,
             Signatures = crypto::ssh::ExtendedSignature,
         >,
         for<'de> A: serde::Deserialize<'de>,
     {
         let entry = store.load(id).map_err(|err| LoadError::Load {
             object: id,
             err: Box::new(err),
         })?;
         Op::try_from(&entry).map_err(|err| LoadError::Encoding { object: id, err })
     }
 }
 impl From<Entry> for Op<Vec<u8>> {