Format names of players who never joined the instance

Reports carry names from the controller, so the reported player, the
reporter or the caller may never have joined this server. The exp_util
formatter asserts the player exists, so those names now fall back to
plain white text. The test stub of the formatter now requires a LuaPlayer
like the real one, which made the existing receiver tests fail before the
fix.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

exp_reports/test/module/env.lua

@@ -23,8 +23,12 @@ return Framework.suite(function(env)
     --- @cast env ExpReports.TestEnv
     env.extend_requires{
         ["modules/exp_util"] = {
-            format_player_name_locale = function(name) return name end,
-            color = { orange_red = "orange_red" },
+            format_player_name_locale = function(player)
+                assert(type(player) == "table", "format_player_name_locale takes a LuaPlayer")
+                return player.name
+            end,
+            format_rich_text_color_locale = function(message) return message end,
+            color = { orange_red = "orange_red", white = "white" },
         },
     }
     env.Reports = assert(loadfile(plugin_root .. "/module/control.lua"))() --- @type ExpReports