seg: add word-level compression enum into data-file header #6958

Job	Run time
test-hive (rpc, compat, 23)	3m 3s
test-hive (engine, auth, 0)	3m 49s
test-hive (engine, api, 0)	7m 4s
test-hive (engine, exchange-capabilities, 0)	3m 43s
test-hive (engine, withdrawals, 0)	6m 46s
test-hive (engine, cancun, 3)	9m 2s
	33m 27s

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