feat: Add high-level Subtensor API with intelligent set_weights

- Add new subtensor module with Subtensor struct (like Python SDK)
- Implement automatic commit-reveal detection and routing:
  - CRv4 (version >= 4): Timelock encryption with DRAND auto-reveal
  - Legacy (version < 4): Hash-based commit-reveal with persistence
  - Direct: When commit-reveal is disabled
- Add SubtensorBuilder for configuration
- Add WeightResponse with tx_hash and metadata
- Add persistence for pending commits (legacy mode)
- Re-export mechanism functions and Subtensor types

Author: EchoBT

src/lib.rs

@@ -7,6 +7,7 @@ pub mod core;
 pub mod crv4;
 pub mod metagraph;
 pub mod queries;
+pub mod subtensor;
 pub mod types;
 pub mod utils;
 pub mod validator;
@@ -72,3 +73,14 @@ pub use crv4::{
     Crv4StateManager, DrandInfo, WeightsTlockPayload, DEFAULT_COMMIT_REVEAL_VERSION,
     DRAND_QUICKNET_GENESIS, DRAND_QUICKNET_PK_HEX, DRAND_ROUND_INTERVAL_SECS,
 };
+
+// Re-export high-level Subtensor API (like Python SDK)
+pub use subtensor::{
+    PendingCommit, Salt, Subtensor, SubtensorBuilder, SubtensorState, WeightResponse,
+    WeightResponseData,
+};
+
+// Re-export mechanism functions from validator
+pub use validator::mechanism::{
+    commit_mechanism_weights, reveal_mechanism_weights, set_mechanism_weights,
+};