Fix comment and remove unreachable char overload per code review

- Fix inaccurate comment: non-literal args use two appends (+= val, += ' '),
  not one concatenated append as the old comment implied.
- Remove the char-specific _AppendRuns overload: all token/keyword constants
  in lex.h are const char* (not char), so no call site ever passes a bare
  char argument; the overload was dead code.

Agent-Logs-Url: https://github.com/Cpp2Rust/cpp2rust/sessions/baf4f5f7-8950-4369-a9c9-708aaed9ad22

Co-authored-by: nunoplopes <2998477+nunoplopes@users.noreply.github.com>

Author: Copilot

cpp2rust/converter/converter.h

@@ -319,7 +319,7 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
   // appended individually.
   // e.g. StrCat("foo", "bar", var1, "xyz") performs:
   //   rs_code_ += "foo bar "   (one append for the merged literal run)
-  //   rs_code_ += var1 + ' '  (one append for the non-literal)
+  //   rs_code_ += val; rs_code_ += ' ';  (two appends for the non-literal)
   //   rs_code_ += "xyz "      (one append for the trailing literal)
   //
   // All _AppendRuns overloads are marked [[gnu::always_inline]] so that Clang
@@ -364,9 +364,9 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
     _AppendRuns(rs_code, _ExtendBuf(buf, val), rest...);
   }
 
-  // Head is NOT a string literal: flush the pending buffer (if any), append
-  // the non-literal argument (value + space), then continue with an empty
-  // buffer.
+  // Head is NOT a string literal: flush the pending buffer (if any), then
+  // append the non-literal argument followed by a space (two separate appends),
+  // and continue with an empty buffer.
   template <std::size_t BufSize, typename T, typename... Rest>
   [[gnu::always_inline]] static void
   _AppendRuns(std::string &rs_code, std::array<char, BufSize> buf,
@@ -378,19 +378,6 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
     _AppendRuns(rs_code, std::array<char, 0>{}, rest...);
   }
 
-  // Head is a single char: flush the pending buffer (if any), then append
-  // the char and its trailing space together as a single 2-byte append.
-  template <std::size_t BufSize, typename... Rest>
-  [[gnu::always_inline]] static void
-  _AppendRuns(std::string &rs_code, std::array<char, BufSize> buf, char val,
-              const Rest &...rest) {
-    if constexpr (BufSize > 0)
-      rs_code.append(buf.data(), BufSize);
-    const char pair[2] = {val, ' '};
-    rs_code.append(pair, 2);
-    _AppendRuns(rs_code, std::array<char, 0>{}, rest...);
-  }
-
   class Buffer {
     std::string partial_code;
     std::string *full_code;