GNU3 demangler: fix sr N-prefix source-name qualifiers and digit-branch substitution pushes

- sr N-prefix branch: guard DemangleUnresolvedType() call with isdigit check
  so GCC-style N <source-name>+ E patterns don't throw on digit-start names
- sr N-prefix branch: push template instantiation (name+args) after template args,
  in addition to the bare name, to keep the substitution table in sync
- sr digit branch: push bare name and template instantiation to substitution table
  so forward references like SK_ resolve correctly

Reduces demangling failures on the corpus from 90 to 4.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: plafosse

demangler/gnu3/demangle_gnu3.cpp

@@ -1784,10 +1784,17 @@ string DemangleGNU3::DemangleExpression()
 		if (m_reader.Peek() == 'N')
 		{
 			m_reader.Consume();
-			out += DemangleUnresolvedType().GetString() + "::";
+			// Standard form: N <unresolved-type> <qualifier-levels>+ E <base>
+			// where <unresolved-type> is T_, Dt, or S.
+			// GCC extension: N <source-name-qualifier>+ E <base>
+			// When the first component is a digit (source name), skip the
+			// unresolved-type and let the loop below handle all qualifiers.
+			if (!isdigit(m_reader.Peek()))
+				out += DemangleUnresolvedType().GetString() + "::";
 			do
 			{
 				out += DemangleSourceName();
+				// Push bare name (before template args) to substitution table.
 				PushType(DemangledTypeNode::NamedType(UnknownNamedTypeClass, _STD_VECTOR<_STD_STRING>{out}));
 				if (m_reader.Peek() == 'I')
 				{
@@ -1796,6 +1803,8 @@ string DemangleGNU3::DemangleExpression()
 					//<tmplate-args>
 					DemangleTemplateArgs(args);
 					out += GetTemplateString(args);
+					// Also push the template instantiation (name+args).
+					PushType(DemangledTypeNode::NamedType(UnknownNamedTypeClass, _STD_VECTOR<_STD_STRING>{out}));
 				}
 				out += "::";
 			}while (m_reader.Peek() != 'E');
@@ -1822,12 +1831,16 @@ string DemangleGNU3::DemangleExpression()
 				hadTemplateArgs = false;
 				const string segName = DemangleSourceName();
 				out += segName;
+				// Push bare name to substitution table.
+				PushType(CreateUnknownType(out));
 				if (m_reader.Peek() == 'I')
 				{
 					vector<string> args;
 					m_reader.Consume();
 					DemangleTemplateArgs(args); // consumes the trailing 'E'
 					out += GetTemplateString(args);
+					// Also push the template instantiation.
+					PushType(CreateUnknownType(out));
 					hadTemplateArgs = true;
 				}
 				out += "::";