[hail] improve import_gtf performance (#8887)
[hail] improve import_gtf performance (#8887)

CHANGELOG: Substantially improve the performance of `import_gtf`.
danking/hail,cseed/hail,hail-is/hail,hail-is/hail,danking/hail,cseed/hail,cseed/hail,cseed/hail,hail-is/hail,danking/hail,cseed/hail,cseed/hail,hail-is/hail,danking/hail,danking/hail,hail-is/hail,danking/hail,hail-is/hail,cseed/hail,hail-is/hail,danking/hail,hail-is/hail,cseed/hail,danking/hail