docs(gfql): add temporal predicates documentation and notebook CI testing

[lmeyerov]

Summary

This PR adds comprehensive documentation for GFQL temporal predicates and introduces notebook CI testing infrastructure.

Changes

Documentation

• GFQL Temporal Predicates Documentation (from previous commits in this branch):
  • Added datetime filtering guide with comprehensive examples
  • Added wire protocol reference for temporal value serialization
  • Added temporal_predicates.ipynb demonstrating date/time filtering with pandas/numpy datetime types
  • Shows usage of gt, lt, between, is_in with temporal values
  • Demonstrates timezone-aware filtering and wire protocol dict usage

CI Infrastructure

• Notebook Testing Framework:
  • Added automated validation for Jupyter notebooks during docs build
  • Structure validation: Ensures notebooks have required fields (e.g., execution_count)
  • Execution validation: Optionally verifies notebooks run without errors
  • Currently validates temporal_predicates.ipynb and layout_tree.ipynb
  • Integrated into GitHub Actions CI pipeline

Fixes

• Fixed temporal_predicates.ipynb structure (added missing execution_count, removed invalid markdown cell outputs)
• Fixed pre-existing PlotterBase.py RST docstring formatting errors that were blocking docs build

Build Improvements

• Added ipykernel==6.29.5 to docs dependencies for notebook execution
• Updated Dockerfile to register Python kernel during build
• Changed docs build script from /bin/sh to /bin/bash for array support

Testing

• Docs build passes with all temporal predicates documentation
• Notebook structure validation runs on every CI build
• Selected notebooks don't require .plot() or register() calls, making them suitable for CI validation

Notes

• This completes the GFQL temporal predicates feature by adding user-facing documentation
• The notebook CI infrastructure ensures our example notebooks remain valid and executable
• Additional notebooks can be added to validation as needed