Add Redis-based one-time download token support

Integrate Redis as a backend for one-time download token validation, with in-memory fallback. Added RedisManager for connection lifecycle, TokenStore for atomic token usage checks, and related configuration via environment variables. Updated download flow to ensure tokens are single-use, and improved API robustness for batch operations. Updated dependencies to include redis and cachetools.

pyproject.toml

@@ -9,6 +9,7 @@ dependencies = [
     "aiohttp>=3.13.2",
     "aiosqlite==0.22.1",
     "argon2-cffi>=25.1.0",
+    "cachetools>=6.2.4",
     "fastapi[standard]>=0.122.0",
     "httpx>=0.27.0",
     "itsdangerous>=2.2.0",
@@ -21,6 +22,7 @@ dependencies = [
     "pytest-xdist>=3.5.0",
     "python-dotenv>=1.2.1",
     "python-multipart>=0.0.20",
+    "redis[hiredis]>=7.1.0",
     "sqlalchemy>=2.0.44",
     "sqlmodel>=0.0.27",
     "uvicorn>=0.38.0",