Remove the first empty line for `uv tree --package foo` (#7885)
## Summary
When using `uv tree --package foo`, an extra empty line appears at the
beginning, which seems unnecessary since `uv tree` without the package
option doesn’t have this. It’s possible that the intention was to add
separation between packages, i.e. the correct implementation shoule be:
```rust
if !std::mem::take(&mut first) {
lines.push(String::new());
}
```
Even if corrected, this extra spacing might be redundant as `uv tree`
doesn’t include these empty lines between packages by default.
```console
$ uv init project
$ cd project
$ uv init foo
$ uv tree
Using CPython 3.12.5
Resolved 2 packages in 1ms
foo v0.1.0
project v0.1.0
$ uv tree --package project
Using CPython 3.12.5
Resolved 2 packages in 1ms
project v0.1.0
```
