refactor(tools): rename rhema-tools-contract to rhema-claw-tools-contract

The crate binds the claw to its client tools, not tools at large,
so it carries the claw's name: package, lib and dep names, the
mock's binary, and the conformance suite's use paths. Specs and
README follow. The tools/contract directory keeps its name, and
no reference to the old name remains.

tools/common/src/lib.rs

@@ -7,7 +7,7 @@
 
 use std::io::Write;
 
-use rhema_tools_contract::{ApiError, CONTRACT_HEADER, CONTRACT_VERSION};
+use rhema_claw_tools_contract::{ApiError, CONTRACT_HEADER, CONTRACT_VERSION};
 use serde::Serialize;
 use serde_json::Value;