Speed up cache size command (#17015)

## Summary

`uv cache size` can be quite slow. Here i use
https://github.com/sharkdp/diskus to walk the cache directory with in
multiple threads.

Add cli option to set the number of threads and default to `
std:🧵:available_parallelism()` or 1.

## Test Plan

Added cli statement with info log test.

I believe this is a fair test, where i set cache dir to a large
directory.

```bash
matthew@matthew-main ~/develop/personal/uv                                                                                                                                                                                                                 [14:17:50]                                                                                                                                                                                                                                       [±cache-size-speed-up ✓▴]
> $ uv cache size --preview-features cache-size -H --cache-dir ~/develop/                                                                                                                                                                   [±cache-size-speed-up ✓▴]
75.7GiB

matthew@matthew-main ~/develop/personal/uv                                                                                                                                                                                                                 [14:18:24]
> $ hyperfine 'uv cache size --preview-features cache-size -H --cache-dir ~/develop/' 'target/debug/uv cache size --preview-features cache-size -H --cache-dir ~/develop/'                                                                  [±cache-size-speed-up ✓▴]
Benchmark 1: uv cache size --preview-features cache-size -H --cache-dir ~/develop/
  Time (mean ± σ):      1.059 s ±  0.014 s    [User: 0.171 s, System: 0.884 s]
  Range (min … max):    1.048 s …  1.097 s    10 runs

Benchmark 2: target/debug/uv cache size --preview-features cache-size -H --cache-dir ~/develop/
  Time (mean ± σ):     413.8 ms ±  17.1 ms    [User: 5789.2 ms, System: 1682.0 ms]
  Range (min … max):   386.3 ms … 441.6 ms    10 runs

Summary
  target/debug/uv cache size --preview-features cache-size -H --cache-dir ~/develop/ ran
    2.56 ± 0.11 times faster than uv cache size --preview-features cache-size -H --cache-dir ~/develop/  
```

Cargo.lock

@@ -1038,6 +1038,15 @@ dependencies = [
  "itertools 0.10.5",
 ]
 
+[[package]]
+name = "crossbeam-channel"
+version = "0.5.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "82b8f8f868b36967f9606790d1903570de9ceaf870a7bf9fbbd3016d636a2cb2"
+dependencies = [
+ "crossbeam-utils",
+]
+
 [[package]]
 name = "crossbeam-deque"
 version = "0.8.6"
@@ -1255,6 +1264,16 @@ dependencies = [
  "windows-sys 0.61.0",
 ]
 
+[[package]]
+name = "diskus"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ec07379c016f78e7ddcd953663b9ed17928ff384928d34d824ed7e463bd3d908"
+dependencies = [
+ "crossbeam-channel",
+ "rayon",
+]
+
 [[package]]
 name = "dispatch2"
 version = "0.3.0"
@@ -3443,9 +3462,9 @@ dependencies = [
 
 [[package]]
 name = "rayon"
-version = "1.10.0"
+version = "1.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b418a60154510ca1a002a752ca9714984e21e4241e804d32555251faf8b78ffa"
+checksum = "368f01d005bf8fd9b1206fb6fa653e6c4a81ceb1466406b81792d87c5677a58f"
 dependencies = [
  "either",
  "rayon-core",
@@ -3453,9 +3472,9 @@ dependencies = [
 
 [[package]]
 name = "rayon-core"
-version = "1.12.1"
+version = "1.13.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1465873a3dfdaa8ae7cb14b4383657caab0b3e8a0aa9ae8e04b044854c8dfce2"
+checksum = "22e18b0f0062d30d4230b2e85ff77fdfe4326feb054b9783a3460d8435c8ab91"
 dependencies = [
  "crossbeam-deque",
  "crossbeam-utils",
@@ -5402,6 +5421,7 @@ dependencies = [
  "clap",
  "console 0.16.1",
  "ctrlc",
+ "diskus",
  "dotenvy",
  "dunce",
  "embed-manifest",

Cargo.toml

@@ -103,6 +103,7 @@ ctrlc = { version = "3.4.5" }
 cyclonedx-bom = { version = "0.8.0" }
 dashmap = { version = "6.1.0" }
 data-encoding = { version = "2.6.0" }
+diskus = { version = "0.9.0", default-features = false }
 dotenvy = { version = "0.15.7" }
 dunce = { version = "1.0.5" }
 either = { version = "1.13.0" }

crates/uv/Cargo.toml

@@ -75,6 +75,7 @@ base64 = { workspace = true }
 clap = { workspace = true, features = ["derive", "string", "wrap_help"] }
 console = { workspace = true }
 ctrlc = { workspace = true }
+diskus = { workspace = true }
 dotenvy = { workspace = true }
 dunce = { workspace = true }
 flate2 = { workspace = true, default-features = false }

crates/uv/src/commands/cache_size.rs

@@ -1,6 +1,7 @@
 use std::fmt::Write;
 
 use anyhow::Result;
+use diskus::DiskUsage;
 
 use crate::commands::{ExitStatus, human_readable_bytes};
 use crate::printer::Printer;
@@ -31,16 +32,9 @@ pub(crate) fn cache_size(
         return Ok(ExitStatus::Success);
     }
 
-    // Walk the entire cache root
+    let disk_usage = DiskUsage::new(vec![cache.root().to_path_buf()]);
-    let total_bytes: u64 = walkdir::WalkDir::new(cache.root())
+
-        .follow_links(false)
+    let total_bytes = disk_usage.count_ignoring_errors();
-        .into_iter()
-        .filter_map(Result::ok)
-        .filter_map(|entry| match entry.metadata() {
-            Ok(metadata) if metadata.is_file() => Some(metadata.len()),
-            _ => None,
-        })
-        .sum();
 
     if human_readable {
         let (bytes, unit) = human_readable_bytes(total_bytes);