Add in operator

[sbundaz]

Issue: #407

This PR adds the in operator.

[JeffersGlass]

In general this looks good to me! A few thoughts:

1. It would be nice to have _dict.__contains__ and _tuple.__contains__ for completeness in the stdlib
2. A bunch of the string methods got moved to App Level (stdlib/_str.spy) earlier this week. For consistency str.__contains__ may want to move there
3. There isn't a firm story around Iterator or Iterable yet... in CPython if there's no __contains__ method it falls back to __iter__ (SPy's __fastiter__?) and then __getitem__ if they exist. This is probably overkill for now, but maybe a good extension for later.

[JeffersGlass]

After a little more testing, I think you'll need to add some additional traps for non-matching types of generic containers.. For instance, this is currently an error:

def main() -> None:
    x = [1,2,3]
    "1" in x

TypeError: mismatched types
  | /workspaces/spy/a.spy:4
  |     print("1" in x)
  |           |_| expected `i32`, got `str`

  | /workspaces/spy/stdlib/_list.spy:364
  |         def __contains__(self, value: T) -> bool:
  |         |______________________________________| function defined here

  | /workspaces/spy/a.spy:4
  |     print("1" in x)
  |           |______| operator::IN called here

Whereas it probably wants to just return False.

[antocuni]

After a little more testing, I think you'll need to add some additional traps for non-matching types of generic containers.. For instance, this is currently an error:

def main() -> None:
    x = [1,2,3]
    "1" in x

TypeError: mismatched types
  | /workspaces/spy/a.spy:4
  |     print("1" in x)
  |           |_| expected `i32`, got `str`

  | /workspaces/spy/stdlib/_list.spy:364
  |         def __contains__(self, value: T) -> bool:
  |         |______________________________________| function defined here

  | /workspaces/spy/a.spy:4
  |     print("1" in x)
  |           |______| operator::IN called here

Whereas it probably wants to just return False.

I'm happy to be convinced otherwise, but I think this should be an error, unless it's list[object] or list[dynamic].

I made the same choice for e.g. ==: 1 == ”hello" it's a TypeError

[antocuni]

@sbundaz sorry it's taking so long to review, I hope to get to it soon!