## Summary
It turns out that _some_ identifiers can contain newlines --
specifically, dot-delimited import identifiers, like:
```python
import foo\
.bar
```
At present, we print all identifiers verbatim, which causes us to retain
the `\` in the formatted output. This also leads to violating some debug
assertions (see the linked issue, though that's a symptom of this
formatting failure).
This PR adds detection for import identifiers that contain newlines, and
formats them via `text` (slow) rather than `source_code_slice` (fast) in
those cases.
Closes https://github.com/astral-sh/ruff/issues/7734.
## Test Plan
`cargo test`
## Summary
Format import statements in all their variants. Specifically, this
implemented formatting `StmtImport`, `StmtImportFrom` and `Alias`.
## Test Plan
I added some custom snapshots, even though this has been covered well by
black's tests.
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## Summary
This PR replaces the `verbatim_text` builder with a `not_yet_implemented` builder that emits `NOT_YET_IMPLEMENTED_<NodeKind>` for not yet implemented nodes.
The motivation for this change is that partially formatting compound statements can result in incorrectly indented code, which is a syntax error:
```python
def func_no_args():
a; b; c
if True: raise RuntimeError
if False: ...
for i in range(10):
print(i)
continue
```
Get's reformatted to
```python
def func_no_args():
a; b; c
if True: raise RuntimeError
if False: ...
for i in range(10):
print(i)
continue
```
because our formatter does not yet support `for` statements and just inserts the text from the source.
## Downsides
Using an identifier will not work in all situations. For example, an identifier is invalid in an `Arguments ` position. That's why I kept `verbatim_text` around and e.g. use it in the `Arguments` formatting logic where incorrect indentations are impossible (to my knowledge). Meaning, `verbatim_text` we can opt in to `verbatim_text` when we want to iterate quickly on nodes that we don't want to provide a full implementation yet and using an identifier would be invalid.
## Upsides
Running this on main discovered stability issues with the newline handling that were previously "hidden" because of the verbatim formatting. I guess that's an upside :)
## Test Plan
None?
Charlie Marsh
Micha Reiser
konsti