Add library metadata files

[brocci]

Summary

Add library.properties and library.json to enable automatic library discovery by Arduino IDE and PlatformIO.
Auto485 is missing the standard Arduino library metadata files required
for automatic discovery by Arduino IDE and PlatformIO.

Changes

• library.properties — Standard Arduino library metadata (name, version, author, architectures, includes, etc.) as defined by the Arduino Library Specification.
• library.json — PlatformIO-compatible metadata for registry-based dependency resolution.

These files have no impact on compilation but are required by toolchains that discover libraries by scanning directories.