Support schema-on-read for PrimitiveWeaver.intWeaver

[Copilot]

This PR implements schema-on-read capability for PrimitiveWeaver.intWeaver, enabling flexible type conversions from various MessagePack types to Int, similar to airframe-codec functionality.

Changes

Enhanced intWeaver.unpack method to support:

• INTEGER types: All MessagePack integer formats (INT8, INT16, INT32, INT64, UINT8, UINT16, UINT32, UINT64, FixInt) with proper overflow handling
• FLOAT types: Safe conversion of whole number doubles/floats within Int range
• STRING types: Parsing of numeric strings to Int with comprehensive error handling
• BOOLEAN types: Standard conversion (true→1, false→0)
• NIL type: Converts to 0 following common convention
• Error handling: Appropriate error messages for unsupported types and invalid conversions

Before:

override def unpack(u: Unpacker, context: WeaverContext): Unit =
  // TODO Schema-on-read support
  context.setInt(u.unpackInt)

After:

override def unpack(u: Unpacker, context: WeaverContext): Unit =
  u.getNextValueType match
    case ValueType.INTEGER => /* handle all integer types */
    case ValueType.FLOAT => /* convert whole numbers safely */
    case ValueType.STRING => /* parse numeric strings */
    case ValueType.BOOLEAN => /* true=1, false=0 */
    case ValueType.NIL => /* nil=0 */
    case other => /* appropriate error */

Testing

Added comprehensive test suite (PrimitiveWeaverTest) with 9 test cases covering:

• ✅ Valid conversions for all supported types
• ✅ Error cases for invalid conversions (fractional floats, non-numeric strings, etc.)
• ✅ Edge cases (Int.MaxValue/MinValue boundaries, overflow scenarios)
• ✅ Cross-platform compatibility (JVM, JS, Native)

All existing tests continue to pass, ensuring backward compatibility.

Impact

• No breaking changes - maintains full backward compatibility
• Enhanced functionality - enables flexible data transformation patterns
• Robust error handling - prevents runtime failures with clear error messages
• Minimal code footprint - surgical changes with maximum impact

Fixes #105.

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[xerial]

context.setNull should be used

[Copilot]

Updated to use context.setNull instead of context.setInt(0) for NIL values. This is more semantically correct as NIL represents absence of value rather than explicit zero. The functional behavior remains the same (NIL → 0) since null.asInstanceOf[Int] returns 0 in Scala. (578b981)

[xerial]

For unknown valuse, we also need to call skipValue of the unpacker to proceed the cursor

[Copilot]

Added u.skipValue call before setting error for unknown value types to properly advance the unpacker cursor. (eeea193)