fix(hop): cuDF-safe label seen-ID tracking

[lmeyerov]

Summary

• replace merge-based seen-marker tracking in hop label paths with engine-native domains (Series/Index + isin)
• avoids pandas Index conversions on cuDF while preserving label semantics
• add hop label regression coverage and changelog entry

Before / After

• Before (cuDF): hop labels could error or sync to host because label tracking used pandas Index conversions.
• After: label tracking stays engine-native.

Example (GFQL)

from graphistry.compute.ast import n, e

# Labeling hop paths triggers the code path fixed here
result = g.chain([
    n(),
    e(hops=2, label_node_hops='nh', label_edge_hops='eh', label_seeds=True),
])

Scope

Affects only hop label tracking (when label_node_hops, label_edge_hops, label_seeds, output_min_hops/output_max_hops, or min_hops > 1 are used).

Testing

• uv run env PYTHONPATH=. pytest graphistry/tests/compute/test_hop.py -q