Jito Block Engine sendBundle (with landing confirmation)

JSON-RPC 2.0 endpoint that submits a bundle to the Jito Block Engine and waits for it to land. Internally calls sendJitoBundle, which simulates the bundle, sends it to https://<region>.mainnet.block-engine.jito.wtf/api/v1/bundles, polls signature status until the first transaction is confirmed (up to ~30s), and retries on failure.

Spec reference: https://docs.jito.wtf/lowlatencytxnsend/#sendbundle

Notes:

• On success the response is HTTP 200 with a result object. On failure the response is HTTP 400 with a JSON-RPC error envelope.
• Bundle size is capped at 5 transactions (Jito limit).
• Transactions must already include a tip instruction; this endpoint does NOT inject tips.
• Transactions must be fully signed (all required signatures present) before submission. Unsigned bundles return HTTP 400 with JSON-RPC INVALID_PARAMS and data.unsignedIndices listing the offending positions.
• This endpoint blocks until the bundle lands or polling/retries are exhausted.