fix(java): skip settlement for error responses (4xx/5xx)

[madisoncarter1234]

Summary

Adds response status code check before settlement in Java PaymentFilter. If the handler returns a 4xx or 5xx status code, settlement is skipped to prevent charging users for failed requests.

Problem

Currently the Java middleware settles payments regardless of whether the handler succeeded or failed. If the handler returns a 500 error, the user is still charged even though they didn't receive the content they paid for.

Go middleware already checks writer.statusCode >= 400 before settlement.
Python middleware already checks response.status_code >= 200 and response.status_code < 300 before settlement.

Changes

• Added response.getStatus() >= 400 check before calling facilitator.settle()
• Added unit tests for 4xx and 5xx response scenarios
• Updated existing tests to mock resp.getStatus() appropriately

Related

• go settlement failure and initOnStart fixes #720 - Go equivalent fix
• V2: next api wrapper #707 - TypeScript settlement failure handling

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