[ty] Add some tricky test cases for the auto-import importer
We don't attempt to fix these yet. I think there are bigger fish to fry.
I came up with these based on this discussion:
https://github.com/astral-sh/ruff/pull/20439#discussion_r2357769518
Here's one example:
```
if ...:
from foo import MAGIC
else:
from bar import MAGIC
MAG<CURSOR>
```
Now in this example, completions will include `MAGIC` from the local
scope. That is, auto-import is involved with that completion. But at
present, auto-import will suggest importing `foo` and `bar` because we
haven't de-duplicated completions yet. Which is fine.
Here's another example:
```
if ...:
import foo as fubar
else:
import bar as fubar
MAG<CURSOR>
```
Now here, there is no `MAGIC` symbol in scope. So auto-import is in
play. Let's assume that the user selects `MAGIC` from `foo` in this
example. (`bar` also has `MAGIC`.)
Since we currently ignore the declaration site for symbols with
multiple possible bindings, the importer today doesn't know that
`fubar` _could_ contain `MAGIC`. But even if it did, what would we do
with that information? Should we do this?
```
if ...:
import foo as fubar
from foo import MAGIC
else:
import bar as fubar
MAGIC
```
Or could we reason that `bar` also has `MAGIC`?
```
if ...:
import foo as fubar
else:
import bar as fubar
fubar.MAGIC
```
But if we did that, we're making an assumption of user intent, since
they *selected* `foo.MAGIC` but not `bar.MAGIC`.
Anyway, I don't think we need to settle on an answer today, but I
wanted to capture some of these tricky cases in tests at the very
least.
