get-sequencer-info should open DB readonly

[jolestar]

Summary

rooch db get-sequencer-info opens RocksDB in read-write mode and collides with a running node, causing lock errors during normal operation.

Impact

Cannot inspect sequencer info while the node is running; command fails due to DB lock contention.

Root cause

Command uses open_rooch_db (read-write) instead of open_rooch_db_readonly.

Proposed fix

Switch to the readonly helper, mirroring other inspection commands:

• Replace open_rooch_db with open_rooch_db_readonly and pass chain_id accordingly.

Acceptance

• Running rooch db get-sequencer-info succeeds while the node is running.
• No RocksDB lock errors; behavior unchanged when node is stopped.