Add Support for Item Deduplication in Batcher

[restareaByWeezy]

Hi!
My team develops no-code community & commerce tool.
Biggest problem for developing no-code tool is client don't know what to fetch, only data knows.
As hundred of duplicated request are called but it is hard to deduplicate requests in component level.
So I highly suggest to add deduplicate feature for handle this problem.

Proposed Solution

Add optional deduplication support to Batcher through new configuration options:

```typescript
interface BatcherOptions<TValue> {
 /**
  * Enable automatic deduplication of items in the batch
  * @default false
  */
 deduplicateItems?: boolean
 
 /**
  * Function to extract a unique key from each item for deduplication
  */
 getItemKey?: (item: TValue) => string | number
}

Benefits

Performance: Reduces unnecessary processing of duplicate items
API Optimization: Fewer redundant network requests
Data Consistency: Ensures only unique items are processed
Flexible: Optional feature that doesn't affect existing behavior

Alternative Approaches

1. User-space deduplication: Users could manually deduplicate before calling addItem, but this:
   Increases boilerplate code
   Loses the temporal relationship between items
   Harder to implement correctly with async scenarios

2. Set-based storage: Always use Set internally, but this:
   Changes semantics for all users (breaking change)
   Doesn't support object-based deduplication easily
   No control over keep-first vs keep-last strategy

Questions

• Are there other deduplication strategies we should consider?
• Should we add a callback like onDuplicate to notify when items are deduplicated?

Looking forward to hearing thoughts on this feature!
I'm happy to work on a PR if this aligns with the project's goals.