[solana] Handle window length timestamp collision

[nvsriram]

• Handle timestamp collision in push_new_window_length function by employing simplified push_checkpoint logic

Function logic:

• Fetch current_index and latest_timestamp
• If latest_timestamp == current_timestamp: overwrite (at current_index - 1) with new window_length
• Else: update next_index, resize if needed, and insert (at current_index) new window_length

[mdulin2]

Looks the same as the regular checkpointing setup. Good fix.