add rpc proxy to dora to avoid problems with non accessible internal rpc nodes

[pk910]

Optimize UI Performance & Add Filtered RPC Proxy

UI Performance Improvements

Fixed excessive RPC requests in validator operation submission forms that were overloading backends with hundreds of users:

Key Optimizations:

• Fixed render-triggered calls: Moved explorer.initControls() to proper useEffect hooks with cleanup
• Added global queue data caching: Shared cache across all form instances eliminates duplicate RPC calls
• Fixed React key prop issue: Removed withdrawalAmount from component keys to prevent unnecessary re-mounts on slider changes
• Reduced polling frequency: Block number polling 5s→10s, queue data polling 15s→20s
• Added proper memoization: useCallback for expensive filter functions

Result: ~95% reduction in RPC requests for validator operations.

Filtered RPC Proxy

Added optional filtered RPC proxy for deployments without public RPC access:

Features:

• Method filtering: Whitelist of safe read-only methods (eth_getStorageAt, eth_getLogs, etc.)
• Rate limiting: Per-IP token bucket (30 req/min, 10 burst by default)
• Parameter validation: Prevents DoS attacks (max 1000 block ranges)
• Request logging: Optional monitoring of all RPC calls
• Automatic frontend integration: When enabled, frontend uses /_rpc endpoint

Configuration:

rpcProxy:
  enabled: true
  upstreamUrl: "http://localhost:8545"
  requestsPerMinute: 30
  burstLimit: 10
  logRequests: true

Endpoint:

• POST /_rpc - Filtered JSON-RPC proxy (separate from API namespace)
• Proper error handling with JSON-RPC 2.0 responses

Use case: Controlled RPC access in private/testing environments without exposing execution clients directly.