Add thiserror instead of exposing eyre anonymous errors

The change here is to make it easier for the consumer to debug the api.
Such that they can `match` on individual errors instead of having to
parse text.

eyre is convenient, but mostly from a consumers perspective

crates/dagger-sdk/Cargo.toml

@@ -19,6 +19,7 @@ serde = { workspace = true }
 serde_json = { workspace = true }
 tracing.workspace = true
 tracing-subscriber.workspace = true
+thiserror.workspace = true
 
 futures = "0.3.28"
 derive_builder = "0.12.0"