fix[lang]: fix precedence in floordiv hint

[cyberthirst]

What I did

• fix Compiler gives incorrect arithmetic hint for decimal division #4077

Commit Message

fix parenthesisation of child exprs in the floordiv hint. previously,
an expression like
```vyper
(x + y) / z
```

could result in a hint suggesting something with incorrect precedence,
like
```vyper
x + y // z
```

this commit conservatively adds parentheses to the hint whenever the
expr in question has child binops.

[cyberthirst]

we don't need to handle braces for AugAssign, right?

vyper/vyper/semantics/types/primitives.py

Line 221 in 767f2da

elif isinstance(node, vy_ast.AugAssign):

[charles-cooper]

thank you!