feat(TokenBalanceController): Dynamic polling interval per chain (#6357)

## Explanation

### Current State
The `TokenBalancesController` currently uses a single global polling
interval for all chains, with the implementation of *WebSocket-based
balance updates** we need **dynamic interval management** per chain (for
websocket-supported chains and for non-supported chains):

- **WebSocket-supported chains** should use minimal polling when
connected (WebSocket provides real-time updates)
- **WebSocket-disconnected chains** need frequent polling as fallback
- **WebSocket connection status changes dynamically**, requiring runtime
interval adjustments
- The current single-interval approach cannot adapt to changing
WebSocket connectivity states

### Solution
This PR introduces **dynamic per-chain polling intervals** that
integrate seamlessly with the **WebSocket service's connectivity
management**:

1. **Dynamic Interval Control**: WebSocket service can adjust polling
intervals in real-time via messenger actions based on connection status
2. **Connectivity-Aware Polling**: Connected chains use long intervals
(WebSocket handles updates), disconnected chains use short intervals
(polling fallback)
3. **Interval Grouping Strategy**: Chains with the same polling interval
are batched together, preserving AccountsAPI efficiency
4. **Messenger Integration**: `updateChainPollingConfigs` action enables
WebSocket service to control intervals dynamically

### ⚠️ **IMPORTANT: This is a Non-Breaking Change**
**All existing code continues to work exactly as it does today**:
- Existing `TokenBalancesController` instantiation without
`chainPollingIntervals` works unchanged
- Default polling behavior remains identical (single global interval)
- All existing APIs (`startPolling`, `stopPolling`, `updateBalances`,
etc.) work as before
- No changes required in MetaMask Extension or any consuming code

The new functionality is **purely additive** and **opt-in**.

### WebSocket Service Integration Flow
```typescript
// WebSocket service manages intervals based on connection status:

// When WebSocket connects, it calls:
this.controllerMessenger.call('TokenBalancesController:updateChainPollingConfigs', {
  '0x1': { interval: 300000 } // 5min - WebSocket handles real-time updates
});

// When WebSocket disconnects from a chain:  
this.controllerMessenger.call('TokenBalancesController:updateChainPollingConfigs', {
  '0x1': { interval: 30000 } // 30s - fallback to frequent polling
});
```

### Technical Implementation
- **Real-time Adaptation**: WebSocket service dynamically adjusts
intervals based on connection health
- **Efficient Batching**: Chains are automatically regrouped by interval
when WebSocket service updates configs
- **Seamless Fallback**: Disconnected chains immediately switch to
frequent polling without manual intervention
- **Connection Recovery**: When WebSocket reconnects, polling
automatically reduces to backup frequency
- **Backward Compatibility**: All existing functionality preserved - new
features only activate when explicitly configured

### Example Runtime Behavior
```typescript
// Current behavior (unchanged):
new TokenBalancesController({ messenger, interval: 30000 })
// → All chains poll every 30s (exactly as today)

// New opt-in behavior:
new TokenBalancesController({ 
  messenger, 
  interval: 30000, // Default fallback
  chainPollingIntervals: { '0x1': { interval: 300000 } } // Ethereum: 5min
})
// → Ethereum polls every 5min, other chains every 30s
```

## Checklist

- [x] I've updated the test suite for new or updated code as appropriate
- Added comprehensive test coverage for per-chain polling intervals and
dynamic updates
- Added tests for interval grouping, runtime configuration changes, and
batching behavior
  - **All existing tests continue to pass unchanged**
- [x] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
  - Added JSDoc comments for messenger actions and configuration options
- [x] I've communicated my changes to consumers by updating changelogs
for packages I've changed, highlighting breaking changes as necessary
- **Note**: **NO BREAKING CHANGES** - this is a purely additive
enhancement
- [x] I've prepared draft pull requests for clients and consumer
packages to resolve any breaking changes
- **Note**: **NO BREAKING CHANGES** - existing code works unchanged,
WebSocket service integration uses new opt-in messenger actions

---------

Co-authored-by: Salim TOUBAL <[email protected]>

Author: Kriys94

packages/assets-controllers/CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- Enhance `TokenBalancesController` with internal dynamic polling per chain support, enabling configurable polling intervals for different networks with automatic interval grouping for improved performance (transparent to existing API) ([#6357](https://github.com/MetaMask/core/pull/6357))
 - Bump `@metamask/base-controller` from `^8.2.0` to `^8.3.0` ([#6465](https://github.com/MetaMask/core/pull/6465))
 
 ## [74.3.2]