Split GFQL temporal text helpers

[lmeyerov]

Closes #1498.

Summary

• Split temporal constructor parsing, value parsing, duration parsing/folding, truncation folding, AST rewrite, and rendering helpers into graphistry.compute.gfql.temporal modules.
• Reduced graphistry.compute.gfql.temporal_text to a small compatibility shim for the historical import path; internal runtime code now imports the domain modules directly.
• Split focused tests into constructor, value, and legacy-shim coverage; updated the Development changelog entry. No temporal semantics changed.

Validation

• python3 -m pytest -q graphistry/tests/compute/gfql/cypher/test_temporal_text.py graphistry/tests/compute/gfql/cypher/test_temporal_constructors.py graphistry/tests/compute/gfql/cypher/test_temporal_value_helpers.py
• python3 -m pytest -q graphistry/tests/compute/predicates/test_temporal_values.py graphistry/tests/compute/gfql/cypher/test_temporal_value_helpers.py -k 'not cudf'
• python3 -m pytest -q graphistry/tests/compute/gfql/cypher/test_lowering.py -k 'temporal or duration'
• ./bin/ruff.sh graphistry/compute/gfql/temporal_text.py graphistry/compute/gfql/temporal graphistry/compute/gfql/row/entity_props.py graphistry/compute/gfql/row/ordering.py graphistry/compute/gfql/row/pipeline.py graphistry/compute/gfql/cypher/lowering.py graphistry/compute/gfql/cypher/result_postprocess.py graphistry/tests/compute/gfql/cypher/test_temporal_text.py graphistry/tests/compute/gfql/cypher/test_temporal_constructors.py graphistry/tests/compute/gfql/cypher/test_temporal_value_helpers.py
• ./bin/typecheck.sh graphistry/compute/gfql/temporal_text.py graphistry/compute/gfql/temporal graphistry/compute/gfql/row/entity_props.py graphistry/compute/gfql/row/ordering.py graphistry/compute/gfql/row/pipeline.py graphistry/compute/gfql/cypher/lowering.py graphistry/compute/gfql/cypher/result_postprocess.py
• python3 import compatibility smoke for legacy temporal_text and new temporal modules
• python3 import-order smoke for constructor-first, folding-first, and legacy-shim-first orders
• git diff --check

Review

• Review skill converged after 3 waves. No blocker/important/suggestion findings.
• Wave 3 specifically covered the shim cleanup, split tests, import cycles, and internal import repointing.

Notes

• Rebased onto origin/master @ f5ef17b after master moved; current head is 0e787a8.
• CI found and the branch fixed a pytest basename collision between the new GFQL values-helper test and the existing predicates temporal values test.
• No dgx-spark RAPIDS run: this is a module split/import cleanup with no DataFrame engine behavior change; focused pandas-compat GFQL CI remains part of the normal PR matrix.