perf: replace SHA-256 with BLAKE3 + add mimalloc global allocator

- Replace SHA-256 with BLAKE3 (~5x faster) for content-addressable hashing
  in dedup_service, file_handler, file_upload_service, chunked_upload_service
- Add mimalloc as global allocator for 10-30% throughput improvement
- sha2 crate retained only for PKCE (OAuth2 standard requirement)
- BLAKE3 produces 64-char hex hashes (same format), no DB schema changes needed

Cargo.toml

@@ -6,6 +6,7 @@ default-run = "oxicloud"
 
 
 [dependencies]
+mimalloc = { version = "0.1.48", default-features = false }
 axum = { version = "0.8.8", features = ["multipart", "http1", "tokio", "macros"] }
 tokio = { version = "1.49.0", features = ["full"] }
 tokio-util = { version = "0.7.18", features = ["io", "codec", "compat"] }
@@ -42,6 +43,7 @@ http-range-header = "0.4"
 image = { version = "0.25", default-features = false, features = ["jpeg", "png", "gif", "webp"] }
 md5 = "0.8.0"
 sha2 = "0.10.9"
+blake3 = "1.8.3"
 hex = "0.4.3"
 http-body-util = "0.1.3"
 percent-encoding = "2.3"