GFQL native types T4: Arrow/type bridge contracts

[lmeyerov]

Summary

• add a stable IR Arrow/type bridge surface in graphistry.compute.gfql.ir.arrow_bridge
• define deterministic strict vs widen coercion semantics for export/import boundaries
• round-trip logical type + schema confidence metadata via Arrow field metadata
• add focused T4 tests and changelog receipt

Changes

• add to_arrow() / from_arrow() helpers for RowSchema + confidence maps
• encode per-field metadata: gfql.logical_type, gfql.schema_confidence
• export bridge symbols from graphistry.compute.gfql.ir package surface
• add tests: graphistry/tests/compute/gfql/test_ir_arrow_bridge.py
• add CHANGELOG entry for GFQL native types T4: Arrow/type bridge contracts and coercion semantics #1312 under Meta: #1046 native type-system staged decomposition program #1262/[FEA] GFQL native type system: schemas, inference, validation, and Arrow representation #1046

Validation

• python -m pytest -q graphistry/tests/compute/gfql/test_ir_arrow_bridge.py
• python -m pytest -q graphistry/tests/compute/gfql/test_ir_m0b_conformance.py graphistry/tests/compute/gfql/test_ir_type_propagation.py
• uv run ruff check graphistry/compute/gfql/ir/arrow_bridge.py graphistry/compute/gfql/ir/__init__.py graphistry/tests/compute/gfql/test_ir_arrow_bridge.py

Closes #1312
Related: #1262 #1046