sausage-plugin part 2: import! with typed clients (sausage_interface::client_rs), TCP endpoints with rpc.endpoint, examples

Part 1 fixes: complete stdout writes, buffered stdin, Rust type names
in schemas, enum variant docs, -32603 for serde errors in handlers,
crate docs and modules. End-to-end check of a generated consumer through
a fake core.

sdk/tests/ui/params.stderr

@@ -5,12 +5,12 @@ error[E0277]: RPC params must be a #[schema] struct with named fields
   |                         ^^^^^^ the trait `Params` is not implemented for `std::string::String`
   |
 help: the trait `Params` is implemented for `sausage_plugin::Empty`
- --> src/lib.rs
+ --> src/discovery.rs
   |
   | impl Params for Empty {}
   | ^^^^^^^^^^^^^^^^^^^^^
-note: required by a bound in `method`
- --> src/lib.rs
+note: required by a bound in `sausage_plugin::method`
+ --> src/discovery.rs
   |
   | pub fn method<P: Params, R: SchemaType>(doc: &mut Value, name: &str, docs: &str) {
   |                  ^^^^^^ required by this bound in `method`
@@ -22,7 +22,7 @@ error[E0277]: RPC params must be a #[schema] struct with named fields
   |                         ^^^^^^ the trait `Params` is not implemented for `std::string::String`
   |
 help: the trait `Params` is implemented for `sausage_plugin::Empty`
- --> src/lib.rs
+ --> src/discovery.rs
   |
   | impl Params for Empty {}
   | ^^^^^^^^^^^^^^^^^^^^^