ruff

1559c73f - Fix fstring formatting removing overlong implicit concatenated string in expression part (#14811)

Fix fstring formatting removing overlong implicit concatenated string in expression part (#14811) ## Summary Fixes https://github.com/astral-sh/ruff/issues/14778 The formatter incorrectly removed the inner implicitly concatenated string for following single-line f-string: ```py f"{'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa' 'a' if True else ""}" # formatted f"{ if True else ''}" ``` This happened because I changed the `RemoveSoftlinesBuffer` in https://github.com/astral-sh/ruff/pull/14489 to remove any content wrapped in `if_group_breaks`. After all, it emulates an *all flat* layout. This works fine when `if_group_breaks` is only used to **add** content if the gorup breaks. It doesn't work if the same content is rendered differently depending on if the group fits using `if_group_breaks` and `if_groups_fits` because the enclosing `group` might still *break* if the entire content exceeds the line-length limit. This PR fixes this by unwrapping any `if_group_fits` content by removing the `if_group_fits` start and end tags. ## Test Plan added test