This PR adds a new IO.copy(InputStream, OutputStream) method to the airframe-control module for copying data between streams on JVM and Native platforms.

Changes

• Added IO.copy(in: InputStream, out: OutputStream): Unit method to the shared IO object
• Method uses 8192-byte buffer (consistent with existing readFully method)
• Properly handles null inputs without throwing exceptions
• Uses withResource for automatic resource management of InputStream
• Calls flush() on OutputStream to ensure buffered data is written
• Added comprehensive tests covering normal operation, edge cases, and large data transfers

Usage

import wvlet.airframe.control.IO
import java.io.{FileInputStream, FileOutputStream}

val input = new FileInputStream("source.txt")
val output = new FileOutputStream("destination.txt")
IO.copy(input, output)

Platform Support

• ✅ JVM: Fully supported
• ✅ Native: Fully supported
• ⚠️ JS: Compiles but InputStream/OutputStream are not practically usable on JavaScript

The method is available on all platforms that support Java IO classes (JVM and Native), while JS compilation succeeds but the classes themselves are not meaningful in a JavaScript context.

Testing

Added comprehensive test suite (IOTest) that verifies:

• Basic copy functionality with various data sizes
• Null input/output stream handling
• Empty stream handling
• Large data transfers (>8KB to test buffer logic)

All tests pass on JVM and Native platforms.

Fixes #396.

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