refactor: migrate project from C++ to Rust

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

Cargo.lock

@@ -0,0 +1,81 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
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+ "proc-macro2",
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+ "unicode-ident",
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+ "thiserror",
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+[[package]]
+name = "wfassoc_dylib"
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+ "thiserror",
+ "wfassoc",
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+
+[[package]]
+name = "wfassoc_exec"
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+dependencies = [
+ "thiserror",
+ "wfassoc",
+]