perf: Migrate Old Guild System gumps to DynamicGump (#2420)

## Summary

Migrates the Old Guild System (pre-AOS guild stones) gumps from the legacy `Gump` class to `DynamicGump`, following the same pattern used for the Quest gump migration in #2416. All concrete gumps now have private constructors gated by static `DisplayTo` entry points (empty-gump rule), and `Singleton => true` is set across the board so reopening a sibling dialog automatically closes the previous one.

**Migrated gumps:**
- `GuildGump` - main guild dialog
- `GuildmasterGump` - guildmaster functions
- `GuildCharterGump` - charter and website display
- `GuildWarGump` - warfare status (kept as player-facing)
- `GuildWarAdminGump` - war menu (retained as player-facing - reachable from `GuildmasterGump`'s WAR button by guildmasters)
- `GuildChangeTypeGump` - Standard/Order/Chaos selection

**Abstract bases:** `GuildListGump` and `GuildMobileListGump` keep their shared list-rendering chrome inside a single concrete `BuildLayout` on the abstract class and expose a `protected abstract void BuildHeader(ref DynamicGumpBuilder builder)` hook for subclasses (replacing the old `Design()` override). This mirrors the abstract-base treatment used for the ML quest base in the quest-gump migration PR.

**Concrete subclasses migrated alongside the abstract bases:**
- `GuildListGump` subclasses: `GuildAcceptWarGump`, `GuildDeclarePeaceGump`, `GuildDeclareWarGump`, `GuildRejectWarGump`, `GuildRescindDeclarationGump`
- `GuildMobileListGump` subclasses: `DeclareFealtyGump`, `GrantGuildTitleGump`, `GuildAdminCandidatesGump`, `GuildCandidatesGump`, `GuildDismissGump`, `GuildRosterGump`

**Cliloc rule:** Every gump bakes per-instance dynamic content (guild names, member names, war declarations, candidate lists), which would defeat `StaticGump<T>` caching. Per the cliloc rule, all are `DynamicGump`.

**External callers updated:** the prompt files (`GuildAbbrvPrompt`, `GuildCharterPrompt`, `GuildDeclareWarPrompt`, `GuildNamePrompt`, `GuildTitlePrompt`, `GuildWebsitePrompt`), `RecruitTarget`, the `Guildstone` item, and the New Guild System `GuildInfoGump`'s Order/Chaos handler all now go through static `DisplayTo` entry points instead of `new XGump(...)`.

Projects/Server/Buffers/SpanWriter.cs

@@ -352,62 +352,62 @@ public ref struct SpanWriter
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void WriteLittleUni(string value) => Write(value, TextEncoding.UnicodeLE);
+    public void WriteLittleUni(ReadOnlySpan<char> value) => Write(value, TextEncoding.UnicodeLE);
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void WriteLittleUniNull(string value)
+    public void WriteLittleUniNull(ReadOnlySpan<char> value)
     {
         Write(value, TextEncoding.UnicodeLE);
         Write((ushort)0);
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void WriteLittleUni(string value, int fixedLength) => Write(value, TextEncoding.UnicodeLE, fixedLength);
+    public void WriteLittleUni(ReadOnlySpan<char> value, int fixedLength) => Write(value, TextEncoding.UnicodeLE, fixedLength);
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void WriteBigUni(string value) => Write(value, TextEncoding.Unicode);
+    public void WriteBigUni(ReadOnlySpan<char> value) => Write(value, TextEncoding.Unicode);
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void WriteBigUniNull(string value)
+    public void WriteBigUniNull(ReadOnlySpan<char> value)
     {
         Write(value, TextEncoding.Unicode);
         Write((ushort)0); // '\0'
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void WriteBigUni(string value, int fixedLength) => Write(value, TextEncoding.Unicode, fixedLength);
+    public void WriteBigUni(ReadOnlySpan<char> value, int fixedLength) => Write(value, TextEncoding.Unicode, fixedLength);
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void WriteUTF8(string value) => Write(value, TextEncoding.UTF8);
+    public void WriteUTF8(ReadOnlySpan<char> value) => Write(value, TextEncoding.UTF8);
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void WriteUTF8Null(string value)
+    public void WriteUTF8Null(ReadOnlySpan<char> value)
     {
         Write(value, TextEncoding.UTF8);
         Write((byte)0); // '\0'
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void WriteAscii(string value) => Write(value, Encoding.ASCII);
+    public void WriteAscii(ReadOnlySpan<char> value) => Write(value, Encoding.ASCII);
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void WriteAsciiNull(string value)
+    public void WriteAsciiNull(ReadOnlySpan<char> value)
     {
         Write(value, Encoding.ASCII);
         Write((byte)0); // '\0'
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void WriteAscii(string value, int fixedLength) => Write(value, Encoding.ASCII, fixedLength);
+    public void WriteAscii(ReadOnlySpan<char> value, int fixedLength) => Write(value, Encoding.ASCII, fixedLength);
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void WriteLatin1(string value) => Write(value, Encoding.Latin1);
+    public void WriteLatin1(ReadOnlySpan<char> value) => Write(value, Encoding.Latin1);
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void WriteLatin1(string value, int fixedLength) => Write(value, Encoding.Latin1, fixedLength);
+    public void WriteLatin1(ReadOnlySpan<char> value, int fixedLength) => Write(value, Encoding.Latin1, fixedLength);
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void WriteLatin1Null(string value)
+    public void WriteLatin1Null(ReadOnlySpan<char> value)
     {
         Write(value, Encoding.Latin1);
         Write((byte)0); // '\0'