Runtime: install the compiled builtin when the interpreter starts #42

What

The maintainer wants @compiled to be a builtin name that needs no import: "파이썬 멀티플랫폼에서는 해당 데코레이터가 기본 키워드가 되도록 할 거니까 특정 패키지 아래로 넣지 마". When python-multiplatform initialises the embedded interpreter, it sets builtins.compiled to an identity decorator. The TypedPython compiler picks out the decorated functions at build time, so at run time the decorator does nothing.

Why

User code must not import a TypedPython package to mark compiled code. On plain CPython the same name comes from a development shim that the typedpython wheel installs (a .pth). The gate learns about it from a __builtins__.pyi extension stub.

Owner

The leader implements this, since it is on the binder initialisation path. TypedPython supplies the shim and the stub.

Done when

A test on each platform: after interpreter initialisation, compiled resolves without an import, and compiled(f) is f holds.