fix(verify.go): Re-order the checks in order of sanity-check severity (#253)

In celestia-node, when a header comes through headersub that may be one
header height behind (due to a slow broadcaster), where our subjective
head is ahead of the incoming net head by 1, we actually catch that
error due to its timestamp:

`
2025-03-19T14:37:16.320+0100 WARN header/sync sync/sync_head.go:181
invalid network header {"height_of_invalid": 26314, "hash_of_invalid":
"D5137A04DD552639D05D9369DE685C1F11B7D85FFCBDA0E54E66E55978C18000",
"height_of_subjective": 26315, "hash_of_subjective":
"6D968C6ED4C8B7B1B5EC1F883E11A02EFD3832DBDF2FD3AB9F9D8F3592227BA0",
"reason": "unordered headers: timestamp '2025-03-19T13:36:53Z' < current
'2025-03-19T13:37:02Z'"}
`

rather than just catching it via the height check. 

This PR reorders the check so that the error is more clear when this
actually happens as it's not really due to unordered timestamps but
rather an older header coming through.

Author: renaynay

verify.go

@@ -53,6 +53,11 @@ func verify[H Header[H]](trstd, untrstd H) error {
 		return fmt.Errorf("%w: '%s' != '%s'", ErrWrongChainID, untrstd.ChainID(), trstd.ChainID())
 	}
 
+	known := untrstd.Height() <= trstd.Height()
+	if known {
+		return fmt.Errorf("%w: '%d' <= current '%d'", ErrKnownHeader, untrstd.Height(), trstd.Height())
+	}
+
 	if untrstd.Time().Before(trstd.Time()) {
 		return fmt.Errorf("%w: timestamp '%s' < current '%s'", ErrUnorderedTime, formatTime(untrstd.Time()), formatTime(trstd.Time()))
 	}
@@ -62,11 +67,6 @@ func verify[H Header[H]](trstd, untrstd H) error {
 		return fmt.Errorf("%w: timestamp '%s' > now '%s', clock_drift '%v'", ErrFromFuture, formatTime(untrstd.Time()), formatTime(now), clockDrift)
 	}
 
-	known := untrstd.Height() <= trstd.Height()
-	if known {
-		return fmt.Errorf("%w: '%d' <= current '%d'", ErrKnownHeader, untrstd.Height(), trstd.Height())
-	}
-
 	return nil
 }