refactor(rust): align workspace with style rules

src/monorepo/BUILD

@@ -0,0 +1,17 @@
+load("@rules_rust//rust:defs.bzl", "rust_library", "rust_test")
+
+rust_library(
+    name = "monorepo",
+    crate_name = "monorepo",
+    srcs = [
+        "monorepo.rs",
+        "workspace.rs",
+    ],
+    visibility = ["//visibility:public"],
+)
+
+rust_test(
+    name = "workspace_test",
+    srcs = ["workspace_test.rs"],
+    deps = [":monorepo"],
+)