Add binary-encoded generative process

[loren-ac]

Summary

• Adds BinaryEncodedProcess, a wrapper that encodes any generative process's vocabulary into fixed-width big-endian binary (MSB first)
• Emits individual bits (vocab_size=2) and defers the underlying state transition until a complete binary word is emitted
• Supports incomplete sequences in probability/log_probability (sequences may end mid-token)
• Unused binary codes (when vocab size is not a power of 2) get probability 0

Test plan

• 35 tests covering properties, observation distributions, state transitions, probability, generation, and wrapping different process types (HMM, GHMM)
• Verified complete binary sequences yield identical probabilities to base process
• Verified decoded generated sequences match base process stationary distribution
• Verified identity behavior when base vocab_size is already 2 (coin process)