test(packs): statistical sampler + mark PackRateConfig [Obsolete]

200k-slot statistical test asserts observed tier rates within +/- 0.5pp
of the seeded SV Classic shape (Bronze=76.5 / Silver=16 / Gold=6 /
Legendary=1.5 on general slots). Marked [Category("Slow")].

PackRateConfig is marked [Obsolete] — no longer consulted by
PackOpenService. Internal callers (GameConfigService / DbContext config
seeding / its own tests) still reference it; they'll go when v1
stabilizes and PackRateConfig is fully retired.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.Database/Models/Config/PackRateConfig.cs

@@ -6,6 +6,7 @@ namespace SVSim.Database.Models.Config;
 /// <see cref="ShippedDefaults"/>, not in the initialiser — see PerSlot docstring.
 /// </summary>
 [ConfigSection("PackRates")]
+[Obsolete("PackRateConfig is no longer consulted by PackOpenService — per-pack rates come from PackDrawTable. Retire once v1 stabilizes.")]
 public class PackRateConfig
 {
     /// <summary>