Implement #162: MADSciClientMixin - #183

Implements issue #162 by creating a reusable mixin class that manages
MADSci client initialization and lifecycle across all components.

## New Features

- **MadsciClientMixin**: Central mixin class for managing all 7 MADSci clients
  - EventClient, ResourceClient, DataClient, ExperimentClient
  - WorkcellClient, LocationClient, LabClient
- Lazy initialization with property-based access
- Flexible configuration via context, explicit URLs, or direct injection
- EventClient sharing across dependent clients
- Comprehensive unit test suite

## Refactored Components

1. **AbstractNode**: Now uses mixin for client management
   - Simplified _configure_clients() method
   - Maintains backward compatibility with logger alias
   - Declares REQUIRED_CLIENTS: ["event", "resource", "data"]

2. **AbstractManagerBase**: Integrated with mixin
   - Updated setup_logging() to use mixin's event_client
   - Inherits all client management functionality
   - Maintains existing API surface

3. **ExperimentApplication**: Uses inherited mixin from AbstractNode
   - Removed manual client initialization
   - Declares OPTIONAL_CLIENTS for additional manager clients
   - Cleaner __init__ method with better documentation

4. **WorkcellManager**: Leverages mixin via AbstractManagerBase
   - Removed manual DataClient/LocationClient creation
   - Uses setup_clients() in initialize()
   - Declares REQUIRED_CLIENTS: ["event", "data", "location"]

## Implementation Details

- All client properties use lazy initialization
- EventClient is always initialized first (other clients depend on it)
- Support for client-specific configuration (retry settings, working directory, etc.)
- Proper type hints with ClassVar for client lists
- Reduced code complexity via helper methods
- All code passes ruff linting and formatting

## Benefits

- **DRY**: Eliminates duplicate client initialization code across components
- **Consistency**: Standardized client setup patterns
- **Maintainability**: Single source of truth for client management
- **Testability**: Easy mock injection for unit tests
- **Flexibility**: Supports multiple configuration strategies
- **Backward Compatible**: No breaking changes to existing APIs

## Testing

- Comprehensive unit test suite for MadsciClientMixin
- Tests cover all client types, initialization patterns, and configuration options
- All modified code passes ruff checks

Closes #162

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Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>