feat(schema): add pretty print helpers

[lmeyerov]

Closes #1633

Summary

• Add experimental pretty() methods for GraphSchema, NodeType, EdgeType, and EdgeTopology with cypher, yaml, and compact formats.
• Override schema dataclass __repr__ to use the compact Cypher-style renderer by default.
• Add graphistry.schema.pretty_print_schema() and top-level graphistry.pretty_print_schema for ergonomic rendering.
• Document usage in the GFQL schema guide and add anchored regression tests for all formats.

Sample output

cypher

(:Person {id: int64, name: string, age: int64})
(:Company {id: int64, name: string})
(:Person)-[:WORKS_AT {since: int64}]->(:Company)
(:Company)-[:CONTRACTS {fee: float64}]->(:Person)

yaml

strict: true
node_id_column: id
edge_columns:
  source: src
  destination: dst
nodes:
  Person:
    labels: Person
    properties:
      id: int64
      name: string
      age: int64
relationships:
  WORKS_AT:
    from: Person
    to: Company
    properties:
      since: int64

compact

GraphSchema(2 node types, 2 edge types, 7 properties)

LOC buckets

• Production: +261 / -2, net +259 LOC
• Tests: +135 / -1, net +134 LOC
• Docs/changelog: +49 / -0, net +49 LOC

Compiler-plan surface touched

No. This is public schema text rendering only. It does not change schema dataclass fields, inference, serialization, binder/compiler behavior, route names, IR metadata, remote schema transport, or planner/verifier contracts.

Notes

• Public viz/schema payload compatibility is not narrowed.
• Arrow/GFQL dtype wrappers render as clean names such as int64 and string; non-null declared Arrow fields render with a compact ! suffix, e.g. int64!.
• Cypher identifiers and YAML scalar names are escaped for non-identifier labels/properties.
• DGX/RAPIDS validation skipped: no DataFrame execution, cuDF, GPU, or algorithm path changed.

Validation

• python3 -m pytest -q graphistry/tests/compute/gfql/test_public_schema.py -> 28 passed
• ./bin/ruff.sh graphistry/schema.py graphistry/__init__.py graphistry/tests/compute/gfql/test_public_schema.py -> passed
• ./bin/typecheck.sh graphistry/schema.py graphistry/__init__.py -> passed
• ./bin/check_docs_latex_unicode.sh -> passed
• git diff --check -> passed
• Review skill converged after wave-1 YAML escaping fix; waves 2 and 3 clean
• Full PR CI green, including RTD preview: https://pygraphistry--1639.org.readthedocs.build/en/1639/

[lmeyerov]

Parking this PR for now. The pretty-printer surfaced a deeper schema-model question that should be decided first: #1644.

Specifically, per-entity declarations probably should not inherit the aggregate table nullable default. A declared NodeType("Person", {"id": int}) likely means Person.id is required/non-null for Person rows, while the merged nodes table column may still be nullable because it is fused across entity types.

Until #1644 is resolved, this PR should not encode nullability display conventions or merge as the canonical schema text surface. Options after #1644:

• update the formatter to reflect the decided per-entity vs aggregate nullability semantics, or
• remove nullability from default pretty output and keep it only in a more explicit/debug format.

CI is green and review skill had converged, but this is now semantically blocked, not technically blocked.