Update cargo to 2024 edition (#842)

Some effects of this change:
- New formatting changes across many files. No functionality changes
should occur from that.
- Calls to `set_env` are considered unsafe, since this only happens in
tests we wrap them in `unsafe` blocks

codex-rs/mcp-types/tests/initialize.rs

@@ -2,10 +2,10 @@ use mcp_types::ClientCapabilities;
 use mcp_types::ClientRequest;
 use mcp_types::Implementation;
 use mcp_types::InitializeRequestParams;
+use mcp_types::JSONRPC_VERSION;
 use mcp_types::JSONRPCMessage;
 use mcp_types::JSONRPCRequest;
 use mcp_types::RequestId;
-use mcp_types::JSONRPC_VERSION;
 use serde_json::json;
 
 #[test]