perf(git): minor performance cleanups

lua/git/diff.lua

@@ -23,16 +23,20 @@ local function attach_index_writer(buf, worktree, path)
                 return
             end
             local sha = vim.trim(hash.stdout or "")
-            local mode = "100644"
-            local ls = vim.system(
-                { "git", "ls-files", "-s", "--", path },
-                { cwd = worktree, text = true }
-            ):wait()
-            if ls.code == 0 and ls.stdout then
-                local m = ls.stdout:match("^(%d+)")
-                if m then
-                    mode = m
+            local mode = vim.b[buf].git_index_mode
+            if not mode then
+                mode = "100644"
+                local ls = vim.system(
+                    { "git", "ls-files", "-s", "--", path },
+                    { cwd = worktree, text = true }
+                ):wait()
+                if ls.code == 0 and ls.stdout then
+                    local m = ls.stdout:match("^(%d+)")
+                    if m then
+                        mode = m
+                    end
                 end
+                vim.b[buf].git_index_mode = mode
             end
             local upd = vim.system({
                 "git",
@@ -116,14 +120,6 @@ end
 ---@param abs_path string
 ---@return integer
 function M.load_file_buf(abs_path)
-    for _, buf in ipairs(vim.api.nvim_list_bufs()) do
-        if
-            vim.api.nvim_buf_is_loaded(buf)
-            and vim.api.nvim_buf_get_name(buf) == abs_path
-        then
-            return buf
-        end
-    end
     local buf = vim.fn.bufadd(abs_path)
     vim.fn.bufload(buf)
     return buf