all components with onSelectionChange have a bad api design

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# Problem Description
The Selection type in Nextui with TypeScript has a few issues that impact its usability and correctness.

# Issues Identified
1. Cannot Retrieve Length
The Selection type, which can be either 'all' or a Set, lacks a consistent way to retrieve its length.
This makes it challenging to perform operations that require knowledge of the number of elements in the selection.

2. Limited Iteration Support
The Selection type currently only offers methods like toString or valueOf in TypeScript.
This limitation prevents convenient iteration over the selection, hindering common use cases.

3. Error in Official Docs Example
The example provided in the official documentation leads to a TypeScript error:
```typescript
Type 'string' is not assignable to type 'SetStateAction>'.ts(2345)
```

Nextui Version: 2.2.9
TypeScript Version: 5.3.3

### 🔦 Context

_No response_

### 💻 Code Sample

https://nextui.org/docs/components/table#controlled-selection

### Version

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### What browsers are you seeing the problem on?

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### If other, please specify

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### What operating system are you using?

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