feat: Add cache header support

[neilberkman]

Closes #9

This PR introduces support for headers on IIIF image responses, allowing for better CDN and browser caching.

Changes

• Adds a option to for a static cache header value.
• Adds an option for dynamically determining the cache header based on the image identifier.
• Implements the cache header logic for all image response types (buffered, file, and stream).
• Includes a new test suite () with comprehensive coverage for the new functionality.
• Updates the to document the new options with usage examples.