chore: bump version to 0.0.21 (#152)

This PR updates the version to 0.0.21 after publishing to PyPI.

## Changes
- Updated version in `pyproject.toml`
- Updated version in `src/claude_code_sdk/__init__.py`

## Release Information
- Published to PyPI: https://pypi.org/project/claude-code-sdk/0.0.21/
- Install with: `pip install claude-code-sdk==0.0.21`

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pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "claude-code-sdk"
-version = "0.0.20"
+version = "0.0.21"
 description = "Python SDK for Claude Code"
 readme = "README.md"
 requires-python = ">=3.10"

src/claude_code_sdk/__init__.py

@@ -269,7 +269,7 @@ async def call_tool(name: str, arguments: dict[str, Any]) -> Any:
     return McpSdkServerConfig(type="sdk", name=name, instance=server)
 
 
-__version__ = "0.0.20"
+__version__ = "0.0.21"
 
 __all__ = [
     # Main exports