Fix Smarter Construction compat for 1.6 cache refactor (#598)

[M-r-A]

Summary

Smarter Construction 1.6 refactored its internal caches from static fields to per-map MapComponents. The existing compat patch in SmarterConstruction.cs still resolved ClosedRegionDetector.cache and other static bindings via AccessTools.StaticFieldRefAccess. On current SC 1.6 builds those fields no longer exist, so DeclaredField returns null and compat init throws:

MPCompat :: Exception loading dhultgren.smarterconstruction: System.ArgumentNullException: Value cannot be null.
Parameter name: fieldInfo
  at HarmonyLib.AccessTools.StaticFieldRefAccess[F] ...
  at Multiplayer.Compat.SmarterConstruction..ctor(ModContentPack mod)

Reported in #598.

Approach

Detect which layout is loaded at init time instead of inferring from a missing static field:

private static bool UsesMapComponentLayout()
{
    var encloseThingsCacheType = AccessTools.TypeByName("SmarterConstruction.Core.EncloseThingsCache");
    return encloseThingsCacheType != null
        && typeof(MapComponent).IsAssignableFrom(encloseThingsCacheType)
        && AccessTools.Method(encloseThingsCacheType, "GetCache", new[] { typeof(Map) }) != null;
}

• 1.6+ path: resolve GetCache(Map) on EncloseThingsCache / PawnPositionCache, clear _cache / _positionCache per map in Find.Maps, reset _lastCacheCleanup to 0.
• Pre-1.6 path: keep existing static field refs (ClosedRegionDetector.cache → nested EncloseThingsCache.cache, static PawnPositionCache fields).
• Assign clearSecondaryCaches once at init (ClearMapComponentCaches or ClearStaticCaches) so GameComponentUtility.FinalizeInit clearing stays branch-free.

Field name fallbacks (_cache / cache, _positionCache / positionCache) retained for minor renames within each layout.

Trade-off

Still uses reflection into private cache fields rather than an upstream SC API (e.g. Compatibility.ClearCachesForMultiplayer()). Acceptable for MP Compat; a public clear hook in rimworld-smarter-construction would be more stable long-term but is out of scope here.

Test plan

• Builds cleanly (Multiplayer_Compat.sln, Debug)
• Game load: log shows MPCompat :: Initialized compatibility for dhultgren.smarterconstruction (no ArgumentNullException)
• MP: start/load colony with Smarter Construction enabled; no compat errors on FinalizeInit
• MP: host + client load same save after a prior session (cache clear on FinalizeInit does not break construction priority / enclose checks)