Allow MMapDirectory+Chunk.BasePtr/Length in private-field-name scan

Chunk's basePtr/length fields are internal-readonly and used outside
the type, so they were renamed to PascalCase per review. The API scan
flags any non-public field that doesn't match camelCase; add an
exception regex for these two as suggested in the review.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: paulirwin

src/Lucene.Net.Tests/Support/TestApiConsistency.cs

@@ -38,7 +38,7 @@ public override void TestProtectedFieldNames(Type typeFromTargetAssembly)
         [TestCase(typeof(Lucene.Net.Analysis.Analyzer))]
         public override void TestPrivateFieldNames(Type typeFromTargetAssembly)
         {
-            base.TestPrivateFieldNames(typeFromTargetAssembly, @"^Lucene\.Net\.Support\.(?:ConcurrentHashSet|PlatformHelper|DateTimeOffsetUtil|Arrays|IO\.FileSupport)|^Lucene\.ExceptionExtensions|^Lucene\.Net\.Util\.Constants\.MaxStackByteLimit|^Lucene\.Net\.Search\.TopDocs\.ShardByteSize|^Lucene\.Net\.Store\.BaseDirectory\.(?:True|False)|CharStackBufferSize$");
+            base.TestPrivateFieldNames(typeFromTargetAssembly, @"^Lucene\.Net\.Support\.(?:ConcurrentHashSet|PlatformHelper|DateTimeOffsetUtil|Arrays|IO\.FileSupport)|^Lucene\.ExceptionExtensions|^Lucene\.Net\.Util\.Constants\.MaxStackByteLimit|^Lucene\.Net\.Search\.TopDocs\.ShardByteSize|^Lucene\.Net\.Store\.BaseDirectory\.(?:True|False)|^Lucene\.Net\.Store\.MMapDirectory\+Chunk\.(?:BasePtr|Length)$|CharStackBufferSize$");
         }
 
         [Test, LuceneNetSpecific]