feat: Add caching layer and batch operations for improved performance

Implement Phase 3 improvements: intelligent caching and batch operations
to significantly enhance SDK performance and usability.

**1. Caching Layer Implementation**

Added complete caching infrastructure with LRU eviction and TTL support:

- `wikijs/cache/base.py`: Abstract BaseCache interface with CacheKey structure
- `wikijs/cache/memory.py`: MemoryCache implementation with:
  * LRU (Least Recently Used) eviction policy
  * Configurable TTL (time-to-live) expiration
  * Cache statistics (hits, misses, hit rate)
  * Resource-specific invalidation
  * Automatic cleanup of expired entries

**Cache Integration:**
- Modified `WikiJSClient` to accept optional `cache` parameter
- Integrated caching into `PagesEndpoint.get()`:
  * Check cache before API request
  * Store successful responses in cache
  * Invalidate cache on write operations (update, delete)

**2. Batch Operations**

Added efficient batch methods to Pages API:

- `create_many(pages_data)`: Batch create multiple pages
- `update_many(updates)`: Batch update pages with partial success handling
- `delete_many(page_ids)`: Batch delete with detailed error reporting

All batch methods include:
- Partial success support (continue on errors)
- Detailed error tracking with indices
- Comprehensive error messages

**3. Comprehensive Testing**

Added 27 new tests (all passing):

- `tests/test_cache.py`: 17 tests for caching (99% coverage)
  * CacheKey string generation
  * TTL expiration
  * LRU eviction policy
  * Cache invalidation (specific & all resources)
  * Statistics tracking

- `tests/endpoints/test_pages_batch.py`: 10 tests for batch operations
  * Successful batch creates/updates/deletes
  * Partial failure handling
  * Empty list edge cases
  * Validation error handling

**Performance Benefits:**
- Caching reduces API calls for frequently accessed pages
- Batch operations reduce network overhead for bulk actions
- Configurable cache size and TTL for optimization

**Example Usage:**

```python
from wikijs import WikiJSClient
from wikijs.cache import MemoryCache

# Enable caching
cache = MemoryCache(ttl=300, max_size=1000)
client = WikiJSClient('https://wiki.example.com', auth='key', cache=cache)

# Cached GET requests
page = client.pages.get(123)  # Fetches from API
page = client.pages.get(123)  # Returns from cache

# Batch operations
pages = client.pages.create_many([
    PageCreate(title="Page 1", path="page-1", content="Content 1"),
    PageCreate(title="Page 2", path="page-2", content="Content 2"),
])

updates = client.pages.update_many([
    {"id": 1, "content": "Updated content"},
    {"id": 2, "is_published": False},
])

result = client.pages.delete_many([1, 2, 3])
print(f"Deleted {result['successful']} pages")
```

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

wikijs/cache/base.py

@@ -0,0 +1,121 @@
+"""Base cache interface for wikijs-python-sdk."""
+
+from abc import ABC, abstractmethod
+from dataclasses import dataclass
+from typing import Any, Optional
+
+
+@dataclass
+class CacheKey:
+    """Cache key structure for Wiki.js resources.
+
+    Attributes:
+        resource_type: Type of resource (e.g., 'page', 'user', 'group')
+        identifier: Unique identifier (ID, path, etc.)
+        operation: Operation type (e.g., 'get', 'list')
+        params: Additional parameters as string (e.g., 'locale=en&tags=api')
+    """
+
+    resource_type: str
+    identifier: str
+    operation: str = "get"
+    params: Optional[str] = None
+
+    def to_string(self) -> str:
+        """Convert cache key to string format.
+
+        Returns:
+            String representation suitable for cache storage
+
+        Example:
+            >>> key = CacheKey('page', '123', 'get')
+            >>> key.to_string()
+            'page:123:get'
+        """
+        parts = [self.resource_type, str(self.identifier), self.operation]
+        if self.params:
+            parts.append(self.params)
+        return ":".join(parts)
+
+
+class BaseCache(ABC):
+    """Abstract base class for cache implementations.
+
+    All cache backends must implement this interface to be compatible
+    with the WikiJS SDK.
+
+    Args:
+        ttl: Time-to-live in seconds (default: 300 = 5 minutes)
+        max_size: Maximum number of items to cache (default: 1000)
+    """
+
+    def __init__(self, ttl: int = 300, max_size: int = 1000):
+        """Initialize cache with TTL and size limits.
+
+        Args:
+            ttl: Time-to-live in seconds for cached items
+            max_size: Maximum number of items to store
+        """
+        self.ttl = ttl
+        self.max_size = max_size
+
+    @abstractmethod
+    def get(self, key: CacheKey) -> Optional[Any]:
+        """Retrieve value from cache.
+
+        Args:
+            key: Cache key to retrieve
+
+        Returns:
+            Cached value if found and not expired, None otherwise
+        """
+        pass
+
+    @abstractmethod
+    def set(self, key: CacheKey, value: Any) -> None:
+        """Store value in cache.
+
+        Args:
+            key: Cache key to store under
+            value: Value to cache
+        """
+        pass
+
+    @abstractmethod
+    def delete(self, key: CacheKey) -> None:
+        """Remove value from cache.
+
+        Args:
+            key: Cache key to remove
+        """
+        pass
+
+    @abstractmethod
+    def clear(self) -> None:
+        """Clear all cached values."""
+        pass
+
+    @abstractmethod
+    def invalidate_resource(self, resource_type: str, identifier: Optional[str] = None) -> None:
+        """Invalidate all cache entries for a resource.
+
+        Args:
+            resource_type: Type of resource to invalidate (e.g., 'page', 'user')
+            identifier: Specific identifier to invalidate (None = all of that type)
+
+        Example:
+            >>> cache.invalidate_resource('page', '123')  # Invalidate page 123
+            >>> cache.invalidate_resource('page')  # Invalidate all pages
+        """
+        pass
+
+    def get_stats(self) -> dict:
+        """Get cache statistics.
+
+        Returns:
+            Dictionary with cache statistics (hits, misses, size, etc.)
+        """
+        return {
+            "ttl": self.ttl,
+            "max_size": self.max_size,
+        }