Optimize RPC calls by batching and deduplication

## Description
Multiple simultaneous proposal fetches can create redundant RPC requests.

## Acceptance Criteria
- Implement request deduplication for identical calls.
- Batch multiple RPC calls into single requests where possible.
- Measure improvement in request count and latency.

## Priority
Medium

## Estimated Effort
Medium

## Dependencies
Issue #146

## Labels
performance, enhancement