RedisTokenStore mutates caller-owned options during initialization

## Summary

`RedisTokenStore#initialize` deletes `:redis` and `:prefix` directly from the caller's options hash. Reusing or freezing a configuration hash therefore changes later behavior or raises `FrozenError`.

## Proposed correction

Duplicate the options hash before consuming constructor-only keys. Candidate: `0c78985a6dc8de3f53ca9b80e2b4065d02311ce2` on 1.17.4/current `main` (`01431c9ecd59e1efc5d262694971ded925044fdc`).

The focused model covers preserved caller state, frozen hashes and explicit Redis objects without a live server. The cumulative suite passes 659 RSpec examples (20 expected pending), 103 Minitest runs /201 assertions and four integration runs /41 assertions, plus RuboCop, syntax, YARD and package/install checks.

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