Add Python 3.13 to CI matrices

[lmeyerov]

Summary

• extend GitHub Actions CPU workflows to Python 3.13/3.14 (lint/types/minimal/core/graphviz) while pinning RAPIDS-dependent CPU + GPU matrices to <= 3.13 until NVIDIA ships 3.14 wheels
• simplify GFQL policy hooks by importing PolicyContext/PolicyException/extract_graph_stats directly with proper typing, fixing the previous lazy loader + flake8/mypy issues
• tighten GFQL postcall context typing + chain_let indentation so lint/mypy stay green across 3.8–3.14 locally and in CI

Testing

• uv run --python cpython-3.8.20-linux-x86_64-gnu --with flake8 flake8 graphistry --count --select=E9,F63,F7,F82 --show-source --statistics
• uv run --python cpython-3.9.23-linux-x86_64-gnu --with flake8 flake8 graphistry --count --select=E9,F63,F7,F82 --show-source --statistics
• uv run --python cpython-3.10.18-linux-x86_64-gnu --with flake8 flake8 graphistry --count --select=E9,F63,F7,F82 --show-source --statistics
• uv run --python cpython-3.11.13-linux-x86_64-gnu --with flake8 flake8 graphistry --count --select=E9,F63,F7,F82 --show-source --statistics
• uv run --python cpython-3.12.10-linux-x86_64-gnu --with flake8 flake8 graphistry --count --select=E9,F63,F7,F82 --show-source --statistics
• uv run --python cpython-3.13.5-linux-x86_64-gnu --with flake8 flake8 graphistry --count --select=E9,F63,F7,F82 --show-source --statistics
• uv run --python cpython-3.14.0b4-linux-x86_64-gnu --with flake8 flake8 graphistry --count --select=E9,F63,F7,F82 --show-source --statistics