Feature: Rich Media for Slack Client

[ArturSlimak]

🚀 Pull Request

📌 Summary

This PR introduces a structured Slack messaging system that enables sending rich, block-based messages.

🧪 What Does This Fix or Improve?

• Bug fix
• New feature
• Performance improvement
• Documentation update
• Other (describe below)

🔍 Changes

• Added block-based messaging system (SlackBlock, SlackElement) with support for:

  • TextBlock, ImageBlock, GifBlock
  • ActionsBlock (for grouping interactive elements)

• Introduced button elements via ButtonElement:

  • Supports both url (link buttons) and actionId (future interaction hooks)

• Implemented builder pattern across the API:

  • SlackMessage.builder()
  • Builders for all blocks and elements
  • Enforced validation rules (no mixing raw/custom blocks, required fields, etc.)

• Added validation framework:

  • SlackValidator<T> interface
  • Validators for all blocks and elements
  • BasicSlackValidators registry
  • SlackBlockValidator with recursive (composite) validation

• Improved error handling:

  • Introduced SlackErrorMapper for errors returned by Slack API
  • Parses Slack API errors into readable, structured messages

• Enhanced BotService:

  • Integrated validation layer
  • Added block building (SlackBlockBuilder)
  • Centralized message sending and error handling

• Support for raw Slack Block Kit (LayoutBlock) usage is hardly changed:

  • Allows advanced/custom Slack blocks
  • Prevents mixing with custom block abstractions

• Refactored and documented codebase with consistent Javadoc:

  • Clear API usage
  • Examples and validation rules included

• Updated README with:

  • Improved usage examples
  • Builder-based approach
  • Rich media

🧪 Testing Steps

TODO. I will open an issue to get some help or cover it after Interactive event handling implementation

📸 Screenshots (if applicable)

Attach images or logs here.

🔗 Related Issues

Partially #9

[shahidfoy]

@ArturSlimak this is looking good so far I plan to try it out on one of my slack channels

would you be able to update the readme.md at the bottom with this info

## N1netails Slack Client Contributors

Thanks to all the amazing people who contributed to N1netails Slack Client! 💙

[![Contributors](https://contrib.rocks/image?repo=n1netails/n1netails-slack-client)](https://github.com/n1netails/n1netails-slack-client/graphs/contributors)

[shahidfoy]

@ArturSlimak make sure the build is passing when running mvn clean install -P release