Git doesn't always write conflict markers of seven characters: the
conflict-marker-size gitattribute overrides that per file, and it is set
for good reasons — for file types whose regular content tends to contain
marker-looking lines, such as documentation about merging, or test
scripts. We hard-code seven characters everywhere we look for markers,
so none of that works.
Prepare for honoring the attribute by threading the marker size through
everything that recognizes a marker, carried on the file model. Nothing
fills it in yet, so we still use git's default size of seven everywhere,
and matching is unchanged: a marker consists of exactly that many marker
characters, and all but the "=======" one are followed by a space and a
label.
In go 1.22, loop variables are redeclared with each iteration of the
loop, rather than simple updated on each iteration. This means that we
no longer need to manually redeclare variables when they're closed over
by a function.
