fix: Harden Advanced Search: crash-safety, autosave, correct results & worker fixes (#2543)

## Summary

Hardens the **Advanced Search** engine (`Projects/UOContent/Engines/Advanced Search/`) — the GM entity finder that fans searches across background worker threads. A code review surfaced 14 defects (A–N), including a shard-crasher reachable from a single admin typo and a path that silently disables autosave for the rest of the shard's uptime. Each behavioral fix ships with a test.

Full `UOContent.Tests` suite: **530/530 green** (21 new AdvancedSearch tests).

## Fixes

### Crash / data-loss
- **A — Shard crash on a malformed Property Test.** `AdvancedSearchThreadWorker.Execute` had no `try/catch` and the worker `Thread` is foreground, so a parse throw (`Hits>abc`, `Layer=onehanded` — `Enum.Parse` was case-sensitive, `Hits>1@` — empty sub-expression indexing) terminated the process. Now: `ParseValue`/`CompareValues` use `TryParse`/`Enum.TryParse(ignoreCase)` and return no-match instead of throwing; the per-entity filter is wrapped in `try/catch` (logs + skips); empty expressions are guarded.
- **C — Overlapping searches corrupt state + brick autosave.** `_threadWorkers`/`_threadId` were `static` but `DoSearch` is an instance method; a second search (double-click / two admins) stomped shared worker state and could leave a drain waiting forever on the shared `AutoResetEvent`, so `AutoSave.SavesEnabled` was never restored. Now: an `Interlocked` re-entrancy guard rejects concurrent searches.
- **G — Autosave restore not guaranteed.** The restore lived only in the success callback. Now it's in a `finally` (plus an outer `catch` covering the synchronous setup and a `catch` on the drain body), so autosave + the guard are always released.

### Wrong results
- **D — `@`/`|` operator precedence.** `a@b|c` evaluated as `a && (b || c)` instead of `(a && b) || c`. OR now binds looser than AND (`AdvancedSearchUtilities.EvaluateBoolean`, unit-tested).
- **E — Descending sort, partial last page rendered blank** (the index decreased in descending mode and the `break` early-out killed the loop). Now a bounded `VisibleCount`-driven loop renders the last page in both directions.
- **F — Deleted entities** were not skipped (ghost rows). Now `DoEntitySearch` skips `entity.Deleted`.
- **N — Reference-type comparisons** threw (`Comparer<T>.Default.Compare` on non-`IComparable`) and compared references to a string. Now equality is by value and ordering is guarded to `IComparable` (no throw).

### Worker perf / hardening
- **H** busy-spin → `Thread.Yield()` in the drain; **I** `GetProperties()` cached per `Type`; **J** `HandleValidInternal` moved behind the cheap map/range/region filters; **K** worker threads are `IsBackground` + `Exit()` tolerates an already-terminated worker; **L** `_filter == null` guard; **M** consistent `Volatile` access on `_pause`/`_exit`.

### Documented
- **B** — the residual worker/event-loop read race is documented on `AdvancedSearchThreadWorker`: workers read live entity state concurrently with the loop, so value-type reads may be stale-but-safe and getter exceptions are swallowed; fully eliminating it would require snapshotting entity fields on the main thread (deferred).

## Notes
- New test-only seams (`TryBeginSearch`/`EndSearch`/`IsSearchInProgress`/`VisibleCount`/`TryParseValue`/`EvaluateBoolean`) are `internal` via the existing `InternalsVisibleTo("UOContent.Tests")`.
- Dead `public ParseValue<T>` removed.
- `ConcurrentDictionary` for the reflection cache is intentional — these workers are genuinely parallel.

Projects/UOContent/Engines/Factions/Core/Faction.cs

@@ -16,7 +16,7 @@ using Server.Targeting;
 namespace Server.Factions;
 
 [CustomEnum(["Minax", "Council of Mages", "True Britannians", "Shadowlords"])]
-public abstract class Faction : IComparable<Faction>
+public abstract class Faction : IComparable<Faction>, ISpanParsable<Faction>
 {
     public const int StabilityFactor = 300;     // 300% greater (3 times) than smallest faction
     public const int StabilityActivation = 200; // Stability code goes into effect when largest faction has > 200 people
@@ -1313,7 +1313,27 @@ public abstract class Faction : IComparable<Faction>
         return null;
     }
 
-    public static Faction Parse(string name)
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static Faction Parse(string s) => Parse(s, null);
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static Faction Parse(string s, IFormatProvider provider) => Parse(s.AsSpan(), provider);
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static bool TryParse(string s, IFormatProvider provider, out Faction result) =>
+        TryParse(s.AsSpan(), provider, out result);
+
+    public static Faction Parse(ReadOnlySpan<char> s, IFormatProvider provider)
+    {
+        if (TryParse(s, provider, out var result))
+        {
+            return result;
+        }
+
+        throw new FormatException($"The input string '{s}' was not in a correct format.");
+    }
+
+    public static bool TryParse(ReadOnlySpan<char> s, IFormatProvider provider, out Faction result)
     {
         var factions = Factions;
 
@@ -1321,13 +1341,15 @@ public abstract class Faction : IComparable<Faction>
         {
             var faction = factions[i];
 
-            if (faction.Definition.FriendlyName.InsensitiveEquals(name))
+            if (s.InsensitiveEquals(faction.Definition.FriendlyName))
             {
-                return faction;
+                result = faction;
+                return true;
             }
         }
 
-        return null;
+        result = null;
+        return false;
     }
 
     public static bool InSkillLoss(Mobile mob) => m_SkillLoss.ContainsKey(mob);