Fix adapter lookup for compound extensions like .jsonl.gz #240

Job	Run time
test (3.11)	2m 26s
discover-templates	4s
test (3.12)	2m 23s
test (3.13)	2m 18s
demo-smoke (templates/01-chatbot-export-synthesis)	29s
demo-smoke (templates/05-batch-build)	16s
demo-smoke (templates/07-chunked-search)	17s
demo-smoke (templates/02-tv-returns)	19s
demo-smoke (templates/03-team-report)	20s
demo-smoke (templates/04-sales-deal-room)	38s
	9m 30s

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