refactor: migrate project from C++ to Rust

- establish basic Rust project layout.
- move all old code into independent directory.

wfassoc_exec/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "wfassoc_exec"
+version = "0.1.0"
+authors = ["yyc12345"]
+edition = "2024"
+description = "The executable configuring Windows file assocation according to user given profile and request."
+license = "SPDX:MIT"
+
+[dependencies]
+thiserror = { workspace = true }
+wfassoc = { path="../wfassoc" }