Use async unzip for local source distributions (#1809)
## Summary
We currently maintain separate untar methods for sync and async, but we
only use the sync version when the user provides a local source
distribution. (Otherwise, we untar as we download the distribution.) In
my testing, this is actually slower anyway:
```
❯ python -m scripts.bench \
--uv-path ./target/release/main \
--uv-path ./target/release/uv \
./requirements.in --benchmark resolve-cold --min-runs 50
Benchmark 1: ./target/release/main (resolve-cold)
Time (mean ± σ): 835.2 ms ± 107.4 ms [User: 346.0 ms, System: 151.3 ms]
Range (min … max): 639.2 ms … 1051.0 ms 50 runs
Benchmark 2: ./target/release/uv (resolve-cold)
Time (mean ± σ): 750.7 ms ± 91.9 ms [User: 345.7 ms, System: 149.4 ms]
Range (min … max): 637.9 ms … 905.7 ms 50 runs
Summary
'./target/release/uv (resolve-cold)' ran
1.11 ± 0.20 times faster than './target/release/main (resolve-cold)'
```
