Simplify VectorStore.delete(List<String> idList) to return void

[sobychacko]

Currently, the delete method returns Optional, which adds unnecessary complexity and is not meaningful for most implementations. The method should instead return void and rely on runtime exceptions to signal errors.

Changes needed:

• Update VectorStore interface to change delete() return type from Optional to void
• Modify all implementing classes to remove boolean return values
• Update related tests to remove Optional assertions

[ilayaperumalg]

Merged as 6035516
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