Support dynamic tempo

[basfroman]

Adds SDK support for the new stateful epoch model introduced in subtensor.

AC for merge:

• bittensor-drand v2.0.0 released
• bittensor-drand updated in SDK dependency in pyproject.toml file
• Subtensor PR#2638 merged

Includes:

Storage getters

• get_last_epoch_block
• get_pending_epoch_at
• get_subnet_epoch_index
• get_activity_cutoff_factor_milli
• get_owner_hyperparam_rate_limit
• get_epoch_schedule_state.

Extrinsics

• set_tempo
• set_activity_cutoff_factor
• root_set_activity_cutoff_factor
• trigger_epoch.

Details

• blocks_until_next_epoch and get_next_epoch_start_block now delegate to the SubnetInfoRuntimeApi runtime API instead of local modulo arithmetic. The tempo parameter is removed from blocks_until_next_epoch.
• commit_timelocked_weights_extrinsic migrated from get_encrypted_commit to get_encrypted_commit_v2 which takes EpochScheduleState for epoch prediction.
• SubnetHyperparameters refactored to a hybrid container that supports v1/v2/v3 chain formats via from_any. Unknown fields spill into hyperparameters dict. Added activity_cutoff_factor field. activity_cutoff is now Optional[int].

New entries:

• EpochScheduleState dataclass in types.py.
• epoch_schedule utility module with blocks_until_next_auto_epoch and is_in_admin_freeze_window.

Breaking changes:

• Requires bittensor-drand>=2.0.0.
• Subtensor.blocks_until_next_epoch and AsyncSubtensor.blocks_until_next_epoch: block is now keyword-only. Callers passing it positionally must update to blocks_until_next_epoch(netuid, block=N).

Related links:

• Subtensor base PR: [Feature] Configurable Tempo & Owner-Triggered Epochs opentensor/subtensor#2638
• Bittensor Drand v.2.0.0 PR: Dynamic tempo support bittensor-drand#71
• e2e tests based on subtensor PR docker image