SK-3118: Restore python-dotenv dependency for flowvault

The bundled common/ module (common/utils/_utils.py) imports `dotenv`, so
`python-dotenv` is a runtime dependency of the flowvault wheel. It was dropped
during the bulk removal on the mistaken belief that only the deleted
utils/_batching.py used it — but common is vendored into the wheel and needs it.
As a result a clean `pip install skyflow-flowvault-python` fails at
`import skyflow` with `ModuleNotFoundError: No module named 'dotenv'`.

Re-add `python-dotenv >= 1.1.0, < 2` (matching skyvault, which kept it).
Verified: the rebuilt wheel declares the dep, and a clean-venv install imports
`skyflow` successfully.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: saileshwar-skyflow

flowvault/setup.py

@@ -89,6 +89,7 @@ def run(self):
         'PyJWT >= 2.12, < 3',
         'cryptography >= 44.0.2',
         'httpx >= 0.21.2',
+        'python-dotenv >= 1.1.0, < 2',
         # NOTE: 'requests' intentionally omitted -- only used today by v2's Connection
         # controller, which isn't part of v3's scope this round.
     ],