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/packages.lock.json

@@ -44,9 +44,9 @@
       },
       "Pidgin": {
         "type": "Direct",
-        "requested": "[3.3.0, )",
-        "resolved": "3.3.0",
-        "contentHash": "2rvIoIogQG1+vqvXCuz1xiAVljaiacG/wCz/TNpN74TzWw+9iSCjhBLf7kVg24sBi6tArRdrcklHq49ovW2NLA=="
+        "requested": "[3.5.1, )",
+        "resolved": "3.5.1",
+        "contentHash": "zU7tkXlF3D6d2GLTjJDomAL3nnl4AwfZvSgSz8D4b+Ry21/clqedYlxBnEAkAU/bkGfEv6uRR7QCdWZUpKrB/g=="
       },
       "SixLabors.ImageSharp": {
         "type": "Direct",