37230f0: Add polling/interval revalidation functionality

This release introduces comprehensive polling capabilities:

• New polling options: refreshInterval, refreshWhenHidden, refreshWhenOffline, dedupingInterval
• Automatic polling management: Polls start/stop automatically with cache lifecycle
• Page visibility awareness: Smart polling that respects page visibility state
• Performance optimizations: Built-in deduplication and memory leak prevention
• New APIs: getPollingInfo(), hasActivePolling(), cleanupPolling()
• Comprehensive examples: Added vanilla JS polling demo

Breaking Changes: None - fully backward compatible

Migration Guide: No migration needed, all new features are opt-in via configuration options.

Add request cancellation functionality with AbortController support

This release introduces comprehensive request cancellation capabilities:

• AbortController integration: Full support for native AbortController API
• Multiple cancellation strategies: Timeout, manual cancellation, revalidation cancellation
• Enhanced fetcher interface: Fetchers now receive AbortSignal parameter
• Cancellation management APIs: cancel(), cancelAll(), isCancelled(), getCancellationInfo()
• Smart cancellation options: abortOnRevalidate, abortTimeout, external signal support
• Error handling: Proper CancellationError with graceful error handling
• Memory management: Automatic cleanup to prevent memory leaks
• Comprehensive examples: Added interactive cancellation demo

Breaking Changes:

• Fetcher function signature now optionally accepts AbortSignal as parameter
• Existing fetchers without AbortSignal parameter continue to work (backward compatible)

Migration Guide:

• Update your fetchers to handle AbortSignal for cancellation support:

  // Before
  const fetcher = async () => fetch('/api/data').then((r) => r.json());
  
  // After (recommended)
  const fetcher = async (signal?: AbortSignal) =>
    fetch('/api/data', { signal }).then((r) => r.json());