Rework puffin sync output to summarize (#81)

This also moves away from using `tracing` for user-facing logging,
instead introducing a new `Printer` abstraction.

Closes #66.

crates/puffin-resolver/src/error.rs

@@ -0,0 +1,21 @@
+use thiserror::Error;
+
+use pep508_rs::Requirement;
+
+#[derive(Error, Debug)]
+pub enum ResolveError {
+    #[error("Failed to find a version of {0} that satisfies the requirement")]
+    NotFound(Requirement),
+
+    #[error(transparent)]
+    Client(#[from] puffin_client::PypiClientError),
+
+    #[error(transparent)]
+    TrySend(#[from] futures::channel::mpsc::SendError),
+}
+
+impl<T> From<futures::channel::mpsc::TrySendError<T>> for ResolveError {
+    fn from(value: futures::channel::mpsc::TrySendError<T>) -> Self {
+        value.into_send_error().into()
+    }
+}