Blocks - Implement subjects on core

[pedronauck]

Description

Implement the Subject::Blocks variant and corresponding Filter methods in the SDK to allow users to subscribe to and filter block data streams. This will enable specific querying and filtering of block information. The implementation should translate filters into the correct NATS subject pattern: blocks.{producer}.{height}.

Tasks

• Add a Blocks variant to the Subject enum if not already present
• Implement a Filter<Subject::Blocks> specialization
• Add the following methods to Filter<Subject::Blocks>:
  • with_producer(producer: String) -> Self
  • with_height(height: BlockHeight) -> Self
• Create a method to convert Filter<Subject::Blocks> to NATS subject strings, following the pattern blocks.{producer}.{height}
• Write unit tests for block filter implementations
• Create integration tests demonstrating block filter usage with Subscription

Technical Details

Ensure each method can be called just once in the builder

• Ensure type safety when creating filters specifically for block subjects
• Implement the builder pattern for block filters to allow for a fluent API
• Define BlockHeight type (likely as a type alias for u32 or similar)
• Optimize the conversion from block filters to NATS subject strings
• Ensure the conversion to NATS subjects correctly follows the blocks.{producer}.{height} pattern

Additional Notes

• The implementation should support usage patterns like:
  Filter::<Subject::Blocks>::new().with_producer("0x1234...").with_height(1000)
• Consider adding additional useful block filtering criteria beyond producer and height
• Ensure consistency with other subject filter implementations in the SDK
• The final NATS subject should correctly represent the filter, e.g., blocks.0x1234....1000

Definition of Done

• Code implemented
• Unit tests written and passing
• Integration tests (if applicable) written and passing
• Documentation updated
• Code reviewed