[M8] reusable libraries: install layout + cargoxx-path deps

tests/e2e/pathDep/greeter/Cargoxx.toml

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+[package]
+name = "greeter"
+version = "0.1.0"
+edition = "cpp23"

tests/e2e/pathDep/greeter/src/lib.cppm

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+export module greeter;
+import std;
+
+export namespace greeter {
+auto hello(std::string_view who) -> std::string {
+    return std::format("Hello from greeter, {}!", who);
+}
+} // namespace greeter