type-time static `StaticPath` types

Checking if files exist statically would be useful
```py
a: StaticPath["foo.txt"] = Path("foo.txt") # error: file doesn't exists
```

Expanding on this we could even statically get the content of the files:
```py
a: StaticPath['foo.txt']
reveal_type(a.read_text()) # "Hello, World!"
```

The issue names no implementation files, tests, or entry points. Start by locating the StaticPath and static file-checking type-analysis code, then establish the intended behavior for missing files and inferred read_text() content. Done should include a decided design and tests covering the proposed examples.

Written by the indexing model from the issue text.