fix(cypher): make conjoined varlen WHERE predicates order-invariant (#1332)

[lmeyerov]

Summary

Fixes #1332: WHERE conjunctions containing variable-length pattern predicates were order-sensitive.

Root cause

ASTNormalizer._rewrite_where_pattern_predicates_to_matches() rewrote multiple positive pattern predicates into an appended MATCH clause, which could couple independent existence checks into a connected pattern shape and make AND operand order observable.

Fix

• Keep multi-positive WHERE pattern predicates in WHERE (skip the appended-MATCH rewrite for that case)
• Lower positive WherePatternPredicate entries directly into independent semi_apply_mark row pre-filters
• Conjoin generated marker columns as row-level filters

Tests

Updated regression coverage in test_lowering.py:

• Existing conjoined bounded-varlen test now checks both operand orders
• Asserts equality across swapped-order queries
• Corrected expected rows to the logical conjunction result for fixture: [{"id":"a"}, {"id":"b"}]

Validation

• PYTHONPATH=. UV_CACHE_DIR=/tmp/uv-cache uv run --no-project --with pytest --with pandas python -m pytest -q graphistry/tests/compute/gfql/cypher/test_lowering.py -k "bounded_variable_length_where_pattern_predicates or conjoined_bounded_varlen_where_predicates_across_edge_types or bounded_variable_length_where_pattern_boolean_wrappers"
• PYTHONPATH=. UV_CACHE_DIR=/tmp/uv-cache uv run --no-project --with pytest --with pandas python -m pytest -q graphistry/tests/compute/gfql/cypher/test_lowering.py -k "where_pattern_predicate"
• ./bin/ruff.sh graphistry/compute/gfql/cypher/ast_normalizer.py graphistry/compute/gfql/cypher/lowering.py graphistry/tests/compute/gfql/cypher/test_lowering.py

Refs #1332