PERFORMANCE: JsonReader/JsonIo - Stream optimization eliminating encode/decode overhead
- Added JsonReader(Reader, ReadOptions) constructor for direct character input
- Updated JavaStringBuilder.parseJson() to use StringReader instead of FastByteArrayInputStream
- Eliminates String → bytes → chars roundtrip in all String-based parsing
- Optimized JsonReader(ReadOptions) and JsonReader(Resolver) constructors to avoid creating dummy streams

IMPROVED: JavaStreamBuilder - Removed redundant InputStream.close()
- Cleaner resource management (JsonReader.close() already closes underlying stream)

DOCUMENTATION: Updated user-guide-writeOptions.md with current API examples

Synchronized with java-util version 4.70.0 for coordinated releases.