perf(snapshots): Parallelize image hashing with rayon

Use rayon's par_iter to hash all images concurrently instead of
sequentially. Also increase the hash read buffer from 8KB to 64KB
to reduce syscall overhead. Reduces hashing time from 5.3s to 0.8s
(6.6x speedup) on a 753-image / 99MB dataset.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: NicoHinderling

src/commands/build/snapshots.rs

@@ -11,6 +11,7 @@ use console::style;
 use itertools::Itertools as _;
 use log::{debug, warn};
 use objectstore_client::{ClientBuilder, ExpirationPolicy, Usecase};
+use rayon::prelude::*;
 use secrecy::ExposeSecret as _;
 use serde_json::Value;
 use sha2::{Digest as _, Sha256};
@@ -231,7 +232,7 @@ fn compute_sha256_hash(path: &Path) -> Result<String> {
     let mut file = std::fs::File::open(path)
         .with_context(|| format!("Failed to open image for hashing: {}", path.display()))?;
     let mut hasher = Sha256::new();
-    let mut buffer = [0u8; 8192];
+    let mut buffer = [0u8; 65536];
     loop {
         let bytes_read = file
             .read(&mut buffer)
@@ -338,9 +339,15 @@ fn upload_images(
     let mut kept_paths = HashMap::new();
     let mut uploads = Vec::with_capacity(images.len());
 
-    for image in images {
-        debug!("Processing image: {}", image.path.display());
+    let hashed_images: Vec<_> = images
+        .into_par_iter()
+        .map(|image| {
+            let hash = compute_sha256_hash(&image.path)?;
+            Ok((image, hash))
+        })
+        .collect::<Result<Vec<_>>>()?;
 
+    for (image, hash) in hashed_images {
         let image_file_name = image
             .relative_path
             .file_name()
@@ -358,7 +365,6 @@ fn upload_images(
             continue;
         }
 
-        let hash = compute_sha256_hash(&image.path)?;
         let key = format!("{org_id}/{project_id}/{hash}");
 
         let mut extra = read_sidecar_metadata(&image.path).unwrap_or_else(|err| {