fix(git): align hunk signs with :diffsplit

lua/git/hunks.lua

@@ -42,15 +42,34 @@ local function resolve_buf(buf)
     return buf and buf ~= 0 and buf or vim.api.nvim_get_current_buf()
 end
 
+---Mirror the hunk-affecting parts of the user's 'diffopt' so the gutter
+---lines up with what `:diffsplit` shows.
+---@return table
+local function diff_opts()
+    local opts = { result_type = "indices", algorithm = "myers" }
+    for _, item in ipairs(vim.split(vim.o.diffopt, ",", { plain = true })) do
+        if item == "indent-heuristic" then
+            opts.indent_heuristic = true
+        else
+            local algorithm = item:match("^algorithm:(.+)$")
+            if algorithm then
+                opts.algorithm = algorithm
+            end
+            local linematch = item:match("^linematch:(%d+)$")
+            if linematch then
+                opts.linematch = tonumber(linematch)
+            end
+        end
+    end
+    return opts
+end
+
 ---@param state ow.Git.Hunks.BufState
 ---@param new_lines string[]
 local function compute_hunks(state, new_lines)
     local old = table.concat(state.index or {}, "\n")
     local new = table.concat(new_lines, "\n")
-    local raw = vim.text.diff(old, new, {
-        result_type = "indices",
-        algorithm = "histogram",
-    })
+    local raw = vim.text.diff(old, new, diff_opts())
     ---@type ow.Git.Hunks.Hunk[]
     local hunks = {}
     if type(raw) ~= "table" then