Support HTTP range requests

[MichaelKreil]

Summary

Add support for HTTP Range requests to enable partial content delivery.

Current State

• The codebase has internal range support in createReadStream() methods (used for reading tile data from .versatiles files)
• However, HTTP Range request headers from clients are not being handled
• The server always returns 200 with full content, never 206 Partial Content

What's Missing

• Parse the Range header from incoming requests
• Respond with 206 Partial Content status for valid range requests
• Set Content-Range header (e.g., bytes 0-999/5000)
• Set Accept-Ranges: bytes header on responses
• Stream only the requested byte range from the file

Use Cases

• Video/audio streaming
• Resumable downloads of large files
• PDF viewers requesting partial content

Relevant Files

• src/lib/responder.ts - needs to handle Range header parsing and 206 responses
• src/lib/bucket/abstract.ts - createReadStream() already supports { start, end } options
• src/lib/bucket/bucket_google.ts - passes range options to Google Cloud Storage
• src/lib/bucket/bucket_local.ts - passes range options to fs.createReadStream()

References

• HTTP Range Requests (MDN)
• RFC 7233 - Range Requests