refactor: remove obsolete format string workaround (#448)

Remove workaround for old Clang/libc++ bug where "<{}>" in format
strings was incorrectly parsed. Modern compilers handle this correctly.

Changes:
- Simplify ListType::ToString() to use direct format string
- Simplify MapType::ToString() to use direct format string
- Remove XXX comments about the workaround

The existing tests will verify this works correctly on current
compilers.

Author: shangxinli

src/iceberg/type.cc

@@ -150,14 +150,7 @@ ListType::ListType(int32_t field_id, std::shared_ptr<Type> type, bool optional)
     : element_(field_id, std::string(kElementName), std::move(type), optional) {}
 
 TypeId ListType::type_id() const { return kTypeId; }
-std::string ListType::ToString() const {
-  // XXX: work around Clang/libc++: "<{}>" in a format string appears to get
-  // parsed as {<>} or something; split up the format string to avoid that
-  std::string repr = "list<";
-  std::format_to(std::back_inserter(repr), "{}", element_);
-  repr += ">";
-  return repr;
-}
+std::string ListType::ToString() const { return std::format("list<{}>", element_); }
 
 std::span<const SchemaField> ListType::fields() const { return {&element_, 1}; }
 Result<std::optional<NestedType::SchemaFieldConstRef>> ListType::GetFieldById(
@@ -213,13 +206,7 @@ const SchemaField& MapType::value() const { return fields_[1]; }
 TypeId MapType::type_id() const { return kTypeId; }
 
 std::string MapType::ToString() const {
-  // XXX: work around Clang/libc++: "<{}>" in a format string appears to get
-  // parsed as {<>} or something; split up the format string to avoid that
-  std::string repr = "map<";
-
-  std::format_to(std::back_inserter(repr), "{}: {}", key(), value());
-  repr += ">";
-  return repr;
+  return std::format("map<{}: {}>", key(), value());
 }
 
 std::span<const SchemaField> MapType::fields() const { return fields_; }