Enhancement: DripFactory::create_stream doesn't reject sender == recipient

[Jaydbrown]

DripFactory::create_stream and create_batch_streams (contracts/factory/src/lib.rs) never check whether recipient == sender. A self-funded stream where the sender is also the recipient is presumably a degenerate/unintended case (they could just not create a stream at all), but nothing in the contract or its validation list rejects it. Worth either explicitly allowing this as documented behavior or adding a check — right now it's silently unspecified.

[Muyideen-js]

@Muyideen-js has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

I'd like to implement a validation check in DripFactory::create_stream that reverts when recipient == sender, and apply the same guard to create_batch_streams by reusing the existing validation logic. I can add a test case to the factory test suite that asserts this revert behavior for both single and batch stream creation.

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[Gabbydunkk]

@Gabbydunkk has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

PLS ASSIGN TO ME

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