`tovector` does not mandate closing `">"`

There's an inconsistency here:

> tovector("<2, 3, 3")
<2, 3, 3>
> lljson.sldecode('"!v<2, 3, 3"')
stdin:1: malformed tagged vector: !v<2, 3, 3
stack backtrace:
[C] function sldecode
stdin:1

However, I'm hesitant to fix this (by making tovector return nil). I feel like maybe tovector should stay a little more lenient than !v, since it's for reading typo-prone notecards

tovector is consistent with (vector) on this point:

llOwnerSay((string)((vector)"<2, 3, 3")); // <2,3,3>

But it's stricter on other points:

> tovector("<2, 3, 3,xx>e1")
nil

llOwnerSay((string)((vector)"<2, 3, 3,xx>e1>")); // <2,3,3>

Originally posted by @tapple in https://github.com/secondlife/slua/pull/61#discussion_r2966891286