Initial project import

tools/v/vlib/v2_toberemoved/README.md

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+## Description
+
+`v2` is a namespace containing a new version of the compiler (still in development).
+
+## Flat AST
+
+`v2.ast` is the default index-based AST graph used by the v2 builder for
+parsing, type checking, markused, and native SSA input:
+
+- `ast.flatten_files(files)` builds `ast.FlatAst` with contiguous `nodes` and `edges`.
+- `ast.legacy_ast_stats(files)` estimates memory/shape metrics for recursive AST files.
+- `flat.stats()` and `flat.count_reachable_nodes()` report flat graph size and reachability.
+- `flat.to_files()` remains available for focused flat-reader roundtrip tests.