Integration: Add smartswitch for rule-based dispatch

[genro]

Problem

Current implementation uses long if/elif chains for dispatching operations:

if backend_type == 's3':
    return S3Backend(...)
elif backend_type == 'local':
    return LocalBackend(...)
elif backend_type == 'memory':
    return MemoryBackend(...)
elif backend_type == 'http':
    return HTTPBackend(...)
# ... many more elif branches

This approach has several issues:

• Verbosity: Long chains hard to read and maintain
• Performance: Linear search through conditions
• Extensibility: Adding backends requires modifying core code
• Type safety: No compile-time validation

Proposed Solution

Integrate smartswitch (from Genro-Libs family) for elegant rule-based dispatch:

Current Pattern

def _create_backend(self, backend_type, config):
    if backend_type == 's3':
        return S3Backend(config)
    elif backend_type == 'local':
        return LocalBackend(config)
    elif backend_type == 'memory':
        return MemoryBackend(config)
    # ... 10+ more elif branches

With Smartswitch

from smartswitch import Switcher

backend_factory = Switcher()

@backend_factory.typerule(backend_type=str)
def create_backend(backend_type: str, config: dict):
    """Default fallback - use fsspec."""
    return FsspecBackend(config)

@backend_factory.valrule(lambda backend_type, config: backend_type == 's3')
def create_s3_backend(backend_type: str, config: dict):
    return S3Backend(config)

@backend_factory.valrule(lambda backend_type, config: backend_type == 'local')
def create_local_backend(backend_type: str, config: dict):
    return LocalBackend(config)

Benefits

1. Cleaner code: Each backend has dedicated factory function
2. Extensibility: Add backends without modifying core
3. Plugin system: External packages can register backends
4. Type safety: Smartswitch validates argument types
5. Performance: O(1) dispatch with pre-compiled rules
6. Testability: Test each backend factory independently

Implementation Plan

1. Add smartswitch to dependencies in pyproject.toml
2. Refactor StorageManager._create_backend() to use Switcher
3. Create decorators for backend registration
4. Update tests (should mostly pass unchanged)
5. Add examples to documentation

Acceptance Criteria

• Remove all if/elif chains for backend selection
• All existing tests pass
• Performance maintained or improved
• Plugin system documented with examples
• Integration tested with custom backends

Priority

Medium - Improves code quality and extensibility

Dependencies

• Requires: smartswitch>=0.1.0 (Genro-Libs family)
• Related: Issue Refactor: Break down long functions (FsspecBackend.capabilities 396 lines) #50 (long functions) - will help reduce function length

References

• Tech review: tech_report/tech_report_001.md (line 265-278)
• Smartswitch docs: https://github.com/genropy/smartswitch
• Pattern: Factory with rule-based dispatch