chore: Enable unparam linter and cover unused *Response results

[ManavSharma142]

Fixes : #3953
I enabled the unparam linter for exported results and exercised previously unused *Response return values in tests.
For the 9 affected methods, I added testNewRequestAndDoFailure blocks to ensure the *Response path is covered.

I also updated the CI config to enable:
unparam:
check-exported: true
and modified apps_test.go accordingly.

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[ManavSharma142]

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