Actually use jemalloc

The uv-performance-memory-allocator is currently optimized out at least on musl due to the crate being otherwise unused (rust-lang/rust#64402), causing musl to not use jemalloc and being slow.

Command:
```
cargo build --target x86_64-unknown-linux-musl --profile profiling
hyperfine --warmup 1 --runs 10 --prepare "uv venv -p 3.12" "target/x86_64-unknown-linux-musl/profiling/uv pip compile scripts/requirements/airflow.in"
```

Before:
```
Time (mean ± σ):      1.149 s ±  0.013 s    [User: 1.498 s, System: 0.433 s]
Range (min … max):    1.131 s …  1.173 s    10 runs
```

After:
```
Time (mean ± σ):     552.6 ms ±   4.7 ms    [User: 771.7 ms, System: 197.5 ms]
Range (min … max):   546.4 ms … 561.6 ms    10 runs
```

Author: konstin

crates/uv/src/bin/uv.rs

@@ -1,3 +1,7 @@
+// Don't optimize the alloc crate away due to it being otherwise unused.
+// https://github.com/rust-lang/rust/issues/64402
+extern crate uv_performance_memory_allocator;
+
 use std::process::ExitCode;
 
 use uv::main as uv_main;