Support gtfparse 3 in the shared pandas 3 annotation stack #484

Topiary capped gtfparse below 3, preventing joint installs with Varcode requiring gtfparse 3.0.2+. The user has authorized a coordinated migration: Topiary #485 requires gtfparse 3.0.2+ and PyEnsembl 2.24.1+, selects pandas explicitly in both expression readers, and verifies both readers against the same known StringTie values. The pandas 2/3 CI matrix and existing downstream integration gates validate the update. Varcode openvax/varcode#579 will require gtfparse 3.0.2+ after Topiary 5.94.2 is published.