feat: configurable maximum stream capacity

[yug49]

Resolves #228

Description

This PR makes the hardcoded MAX_BUFFERED_MESSAGES constant configurable via a new max_stream_capacity builder method, allowing users to tune the internal channel buffer sizes based on their specific use case. The MAX_BUFFERED_MESSAGES constant (50,000) was previously hardcoded and used for both mpsc::channel and broadcast::channel capacities.

Changes

• Added max_stream_capacity field to BlockRangeScanner, ConnectedBlockRangeScanner, and BlockRangeScannerClient
• Added max_stream_capacity() builder method to EventScannerBuilder for all scanner modes
• Updated handle_stream() to accept configurable capacity parameter
• All internal channel creations now use the configurable capacity
• Default value remains 50,000 for backward compatibility

[LeoPatOZ]

Resolved in:
#266