refactor(git): centralize registrations, defer submodule loads

lua/git/diff.lua

@@ -185,31 +185,4 @@ function M.split(opts)
     place_pair(buf, cur_buf, true, opts.vertical)
 end
 
-function M.setup()
-    local function diff_split_cmd(vertical)
-        return function(opts)
-            M.split({
-                rev = opts.args ~= "" and opts.args or nil,
-                vertical = vertical,
-            })
-        end
-    end
-
-    vim.api.nvim_create_user_command(
-        "Gdiffsplit",
-        diff_split_cmd(true),
-        { nargs = "?", desc = "Diff against <rev>" }
-    )
-    vim.api.nvim_create_user_command(
-        "Gvdiffsplit",
-        diff_split_cmd(true),
-        { nargs = "?", desc = "Diff against <rev> (vertical split)" }
-    )
-    vim.api.nvim_create_user_command(
-        "Ghdiffsplit",
-        diff_split_cmd(false),
-        { nargs = "?", desc = "Diff against <rev> (horizontal split)" }
-    )
-end
-
 return M