test(gfql): harden open-range bindings coverage (#880) - #1018

Summary

• follow on from fix(gfql): preserve open-range bindings serialization (#880) #1016 with broader open-range bindings coverage around [FEA] GFQL bindings_table (row bindings) from chain using Yannakakis prune #880
• add AST serialization coverage for bounded, reverse, undirected, and output-slice range payloads
• DRY the bindings-table tests by deriving direct rows(binding_ops=...) payloads from native match ops and reusing shared graph fixtures

Validation

• python3.12 -B -m pytest -q graphistry/tests/compute/test_ast.py graphistry/tests/test_compute_chain.py -k "range or ChainBindingsTable"
• python3.12 -B -m pytest -q graphistry/tests/compute/gfql/cypher/test_lowering.py -k "is6_open_range_continuation_projection_shape"

Scope

• test-only follow-on
• no runtime changes