feat(diff): Add the diff_history command (#97)

This new command is natively implemented by both the `codediff` and `diffview` backends allowing to easily navigate the changes between two revsets while diffing the. 

It also gives a new `:J diff_hisotyr` command that optionally takes a range of revsets formatted `<rev1>..<rev2>` otherwise it prompts the user for the range.

lua/jj/core/parser.lua

@@ -229,4 +229,20 @@ function M.parse_annotation_line(line)
 	return result
 end
 
+-- Given a range with the format "left..right", parse and return the two revisions
+--- @param range_str string The range string to parse (e.g., "left..right")
+--- @return {left: string, right: string}|nil A table
+function M.parse_diff_range(range_str)
+	if not range_str then
+		return nil
+	end
+
+	local left, right = range_str:match("^(%S+)%.%.(%S+)$")
+	if left and right then
+		return { left = left, right = right }
+	end
+
+	return nil
+end
+
 return M