chore(deps): bump Pidgin from 3.3.0 to 3.5.1

Catches up the only direct NuGet dependency that drifted behind on
the v1.0.0 standalone cut. The bump includes:

- 3.4.0: AnyCharExcept performance optimisation for single-char inputs
- 3.5.0: incremental parsing API in Pidgin.Incremental, public Expected
  constructors, SequenceTokenParser performance improvement
- 3.5.1: CIString Unicode handling fix (relevant for non-ASCII
  channel/tab names)

No security advisory drove this; rolling forward to align v1.0.0 with
the current upstream of every direct dependency. dotnet restore +
Release build verified locally, packages.lock.json regenerated.

HellionChat/HellionChat.csproj

@@ -28,7 +28,7 @@
              without a major bump on the managed wrapper. -->
         <PackageReference Include="SQLitePCLRaw.lib.e_sqlite3" Version="3.50.3" />
         <PackageReference Include="morelinq" Version="4.4.0" />
-        <PackageReference Include="Pidgin" Version="3.3.0" />
+        <PackageReference Include="Pidgin" Version="3.5.1" />
         <PackageReference Include="SixLabors.ImageSharp" Version="3.1.12" />
     </ItemGroup>