log: cache diffopts instance
It appears that calling patch.diff*opts() repeatedly has some cost.
$ hg log -T '{rev}\n' -R mercurial --time > /dev/null
(orig) time: real 4.430 secs (user 4.370+0.000 sys 0.050+0.000)
(new) time: real 1.950 secs (user 1.880+0.000 sys 0.060+0.000)
'diffopts or {}' isn't necessary as patch.diff*opts() accepts opts=None.
# See http://EditorConfig.org for the specification
root = true
[*.py]
indent_size = 4
indent_style = space
trim_trailing_whitespace = true
[*.{c,h}]
indent_size = 8
indent_style = tab
trim_trailing_whitespace = true