chore: modernize deps for redis 5/6 and Prefect 3.x compatibility

- Update Python minimum to ^3.10, drop 3.8/3.9 support
- Widen redis constraint to >=5.0.8,<7.0.0
- Bound fastapi to >=0.100.0,<1.0.0
- Raise typing-extensions to >=4.10.0,<5.0.0
- Remove importlib-metadata (stdlib in Python 3.10+)
- Update ruff (>=0.4.0), mypy (>=1.5.0), coverage (>=7.0,<9.0)
- Migrate ruff config to [tool.ruff.lint] section
- Update linter target versions to py310
- Update tox matrix to py310-py313
- Update CI matrix to 3.10-3.14
- Add Hypothesis property-based tests for Redis backend and JsonCoder

Author: wolf-j3blair

.github/workflows/ci-cd.yml

@@ -41,7 +41,7 @@ jobs:
       - lint
     strategy:
       matrix:
-        python: ["3.8", "3.9", "3.10", "3.11"]
+        python: ["3.10", "3.11", "3.12", "3.13", "3.14"]
       fail-fast: false
 
     name: "Test on Python ${{ matrix.python }}"