feat: Add configurable max_request_line_size to handle 414 errors

[hellosunghyun]

Summary

This PR adds a configurable max_request_line_size option to handle 414 (URI Too Long) errors that occur with very long continuation tokens in API requests.

Problem

Users are experiencing 414 errors when accessing channel videos with long continuation tokens. The default HTTP request line size limit (8KB) is insufficient for some YouTube continuation tokens, which can be extremely long.

Example error:

414 Client Error: URI Too Long for url: http://localhost:8080/api/v1/channels/UChQ-VMvdGrYZxviQVMTJOHg/videos?sort_by=newest&continuation=4qmFsgLT...

Solution

• Added max_request_line_size configuration option to the Config class
• Modified server initialization to apply the custom limit if configured
• Provided clear documentation and examples for both config.yml and environment variable usage

Configuration

Users can now configure the limit in three ways:

1. In config.yml:

max_request_line_size: 16384  # 16KB

2. Via environment variable:

INVIDIOUS_MAX_REQUEST_LINE_SIZE=16384

3. In docker-compose.yml:

environment:
  INVIDIOUS_MAX_REQUEST_LINE_SIZE: 16384

Default Behavior

• The default behavior remains unchanged (8KB limit)
• Only users experiencing 414 errors need to configure this option
• Conservative default ensures security for public instances

Testing

• Tested with long continuation tokens that previously caused 414 errors
• Verified that the configuration is properly applied from all sources (config.yml, env var)
• Confirmed that default behavior is maintained when option is not set

Security Considerations

• Added documentation warning about increasing this value on public instances
• The option is intentionally not enabled by default to maintain security posture

This change provides a flexible solution for users experiencing URL length issues without affecting existing installations.

Fixes issues related to long continuation tokens in channel video pagination.