Stop burning miner emissions: normalize distributed rewards to 100%

[anderdc]

Why

Subnet emission on Bittensor scales with price × (1 - miner_burn) — every unit of weight routed to the recycle UID shrinks the whole subnet's emissions. We were burning the full penalty shortfall (ineligible holders, capacity < 1, fill_ratio < 1, empty direction buckets), which regularly amounted to a large slice of the pool.

What

The reward formula is untouched: eligible × pool × crown_share × capacity × fill_ratio. The change is only what happens to the shortfall — instead of topping up RECYCLE_UID, it is left undistributed, and set_weights' existing L1 normalization stretches the distributed mass to 100% of emissions. All penalties keep their full relative bite (ratios between miners are unchanged); the mass a penalized miner forfeits now flows pro-rata to the miners who performed instead of burning.

• calculate_miner_rewards: recycle top-up removed; the scoring trace now logs undistributed=… with the same cause diagnostics.
• Halt: scores are frozen (no update_scores call) so pre-halt weights persist on chain, instead of routing the full pool to the recycle UID. _flush_halt_window dashboard semantics unchanged.
• set_weights empty/NaN fallback: skips the round (previous on-chain weights persist) instead of burning — bittensor's uniform-1/n fallback is still avoided.
• build_halted_rewards deleted; RECYCLE_UID kept in constants (documents the owner UID; tests assert it receives nothing).

Incentive notes

• Hard gates (eligibility, can_fund, executability band) are unaffected — a gated miner still earns absolute zero, and its share flows to other miners, never back to it.
• Soft multipliers become relative rather than absolute: a penalized miner's loss is its competitors' gain. The one regression surface is a low-competition regime where a dominant operator's fleet could coast — worth watching in the scoring traces (undistributed= line) after deploy.

Tests

795 passed (full suite). Recycle-pinning tests rewritten to assert the new invariant: nothing lands on RECYCLE_UID, reward sum equals distributed mass only, halt freezes scores.