Fix URL percent-encoding using space-padding instead of zero-padding

[bysiber]

Summary

URL percent-encoding in Page.links uses %2x format which pads with a space instead of a zero for characters with ordinal values < 16.

Problem

The format string '%%%2x' produces space-padded hex values:

>>> '%%%2x' % 10
'% a'   # invalid URL encoding

>>> '%%%02x' % 10
'%0a'   # correct URL encoding

Characters like newline (0x0a), tab (0x09), etc. matched by _clean_re would be encoded as % a, % 9, etc. — these are not valid percent-encoded sequences per RFC 3986 and would break URL parsing.

Fix

Change %2x to %02x to zero-pad the hex value.