Remove unused internal/mock.NewSampler dead code

[thumbrise]

PR #13 replaces internal/mock.NewSampler with a local staticSampler in the tests. No other files reference mock.NewSampler (confirmed via grep). The file internal/mock/sampler.go appears to be unused dead code and can be safely removed.

Action:

• Remove the dead code file or confirm its status.

Reference: #13 (comment)

[thumbrise]

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