Improve error message for unsupported (future) version numbers

[jorisdral]

lsm-tree/lsm-tree/src-core/Database/LSMTree/Internal/Snapshot/Codec.hs

Lines 222 to 230 in 934503f

	instance Decode SnapshotVersion where
	decode = do
	_ <- decodeListLenOf 1
	ver <- decodeWord
	case ver of
	0 -> pure V0
	1 -> pure V1
	2 -> pure V2
	_ -> fail ("Unknown snapshot format version number: " <> show ver)

It could probably say unsupported rather than unknown and have a helpful message about it being a future version

[mwihoti]

I addressed in #875. The fail in Decode SnapshotVersion now uses the message from the new SnapshotVersionUnknownError: it says the version is unsupported, lists the versions this library supports, and notes the snapshot was most likely written by a newer version.