docs(notebooks): Update GFQL demo notebooks to use gfql() instead of chain()

[lmeyerov]

Summary

This PR updates all GFQL demo notebooks to use the new gfql() and gfql_remote() methods instead of the deprecated chain() and chain_remote() methods.

Stacked on PR #751

This PR is stacked on top of PR #751 (Let matchers support) and should be merged after #751.

Changes

Updated 5 notebooks in demos/gfql/:

Method Replacements

• ✅ benchmark_hops_cpu_gpu.ipynb: 31 .chain() → .gfql()
• ✅ gfql_remote.ipynb:
  • 1 .chain() → .gfql()
  • 8 .chain_remote() → .gfql_remote()
  • Text references updated
• ✅ gfql_validation_fundamentals.ipynb: 6 .chain() → .gfql()
• ✅ GPU_memory_consumption_tutorial.ipynb: 1 .chain() → .gfql()
• ✅ temporal_predicates.ipynb: 7 .chain() → .gfql()

Also Updated

• Code examples in markdown cells
• References to chain_remote() and chain_remote_shape() in documentation text

Related

• Follows API changes from PR docs(gfql): Rename chain() to gfql() throughout documentation #748 (chain→gfql renames in docs)
• Aligns with PR docs(gfql): Add Call/Let/Ref documentation (Part 2 of PR #719 improvements) #750 (documentation improvements)
• Part of ongoing GFQL documentation cleanup from PR docs(gfql): Consolidated GFQL documentation improvements #719

Testing

• Notebooks syntax is valid
• Examples use correct new API

This completes the chain→gfql migration for all demo notebooks.