Improve error handling in KeyvDataLoader class

After reviewing the code, I noticed potential improvements in the error handling logic of the KeyvDataLoader implementation.

### Issues
1. The current implementation doesn't properly handle errors that might occur when interacting with the cache layer.
2. There's no fallback mechanism if the cache fails but the database is available.

### Proposed Solution
1. Add try/catch blocks for cache operations to ensure cache errors don't break the entire functionality:

```typescript
// Example improvement for the set cache entries section
try {
await Promise.all(
entries.map((entry) =>
this.cache.set(entry.key, entry.value, entry.ttl)
)
);
} catch (error) {
// Log the error but continue execution
console.error('Failed to set cache entries:', error);
// Potentially add a cache health flag for future operations
}
```

2. Add a fallback option in constructor:

```typescript
export interface KeyvDataLoaderOptions {
// ... existing options

/**
* If true, fallback to batch loading on cache errors
*/
fallbackOnCacheError?: boolean;
}
```

These changes would make the library more resilient to cache layer failures and improve the overall reliability.