stats.lua: display HDR peak in nits

The value of `sig-peak` is relative to the SDR peak. This is not
a problem when used inside the player, but the `HDR peak` in stats
should display human-readable information.
So change to return the actual nits value of HDR.
Closed mpv-player#10127

player/lua/stats.lua

@@ -737,7 +737,7 @@ local function add_video(s)
     local hdrpeak = r["sig-peak"] or 0
     local hdrinfo = ""
     if hdrpeak > 1 then
-        hdrinfo = " (HDR peak: " .. format("%.2f", hdrpeak) .. ")"
+        hdrinfo = " (HDR peak: " .. format("%.2f", hdrpeak * 203) .. " nits)"
     end
 
     append(s, r["gamma"], {prefix="Gamma:", suffix=hdrinfo})