Add Tetris piece-randomizer ε-machines

[Autoplectic]

Summary

• Add unifilar ε-machine constructors for Tetris spawn algorithms: IID, idealized NES (one reroll), Guideline 7-bag, TGM-style history (tetris_tgm / tetris_tgm2), and the Game Boy 1989 bitwise-OR RNG.
• Document the catalog in docs/examples.rst with wiki citations; omit TGM3's 35-pool drought randomizer because the state space is millions of configurations.
• Cover exact NES/bag identities and TGM/GB smoke checks in tests/test_tetris.py without registering the 2401-state machines on process_list.

Test plan

• pytest tests/test_tetris.py (14 tests: NES 1/28 and 9/56, bag entropy rate log2(7!)/7, TGM history avoidance, Game Boy L-rarest)
• from sofic.examples import tetris_iid, tetris_nes, tetris_bag, tetris_tgm and validate() each small constructor
• Confirm constructors are not on sofic.examples.processes.process_list

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