fix: pass a boxed cause through instead of restating it

The four errors that carry a cause boxed, because the trait they come
from is implemented past a crate boundary, each rendered it with
`#[snafu(display("{source}"))]`. That renders the cause as the wrapper's
own message *and* still reports it from `Error::source()`, so every chain
the cause appears in shows it twice:

    Error: unable to access network 'local', is it running?

    Caused by:
        0: the local network for this project is not running
        1: the local network for this project is not running

`#[snafu(transparent)]` is what these want. Display still forwards to the
cause, so the message is the same, but `source()` returns the cause's own
source rather than the cause, and the wrapper stops being a link in the
chain. Nothing below it is lost: a cause with sources of its own still
contributes all of them.

`LazyAgentError` was hand-written to do exactly this before it became a
derive, down to a comment reading "as `snafu(transparent)` would", so for
that one this is a restoration.

Author: adamspofford

crates/icp/src/agent.rs

@@ -59,7 +59,7 @@ impl<'a> LazyAgent<'a> {
 /// cause is carried whole and displayed as itself rather than being restated
 /// here.
 #[derive(Debug, Snafu)]
-#[snafu(display("{source}"))]
+#[snafu(transparent)]
 pub struct LazyAgentError {
     pub source: Box<dyn Error + Send + Sync + 'static>,
 }

crates/icp/src/canister/recipe/mod.rs

@@ -43,7 +43,7 @@ pub struct Fetched {
 /// project. This layer knows only that it can fail, so the cause is carried
 /// whole and displayed as itself.
 #[derive(Debug, Snafu)]
-#[snafu(display("{source}"))]
+#[snafu(transparent)]
 pub struct ResolveError {
     pub source: Box<dyn std::error::Error + Send + Sync + 'static>,
 }

crates/icp/src/canister/wasm.rs

@@ -13,7 +13,7 @@ use crate::prelude::*;
 /// request and a write to a cache outside the project. This layer knows only
 /// that it can fail, so the cause is carried whole and displayed as itself.
 #[derive(Debug, Snafu)]
-#[snafu(display("{source}"))]
+#[snafu(transparent)]
 pub struct FetchError {
     pub source: Box<dyn std::error::Error + Send + Sync + 'static>,
 }

crates/icp/src/network/mod.rs

@@ -330,7 +330,7 @@ impl From<Mode> for Configuration {
 /// the user needs to be told, so the cause is carried whole and displayed as
 /// itself rather than being restated here.
 #[derive(Debug, Snafu)]
-#[snafu(display("{source}"))]
+#[snafu(transparent)]
 pub struct AccessError {
     pub source: Box<dyn std::error::Error + Send + Sync + 'static>,
 }