Add an offline tiny-model Transformers integration test

[DaBestCode]

Add an end-to-end generation test using a tiny randomly initialized decoder model so CI exercises the public randkv.transformers.generate call without downloading a checkpoint.

Acceptance criteria:

• Construct the model and tokenizer inputs locally; no network access.
• Generate enough tokens to trigger at least two eviction rounds.
• Assert the configured cache bound and monotonic absolute position tracking.
• Run on CPU in the existing Python 3.10/3.13 matrix.
• Keep the test deterministic and under 10 seconds per CI job.