Improve slashing spend core logic

[gusin13]

@gitferry had suggested some improvements in the btc notifications in a previous chat few weeks ago.

Problem - Currently we register to btc notifications on certain triggers.

• When indexer receives babylon event delegation expired - then we register spend notification for staking tx ref
• When indexer receives babylon event early unbonding - then we register spend notification of unbonding tx ref

Ideally indexer should not wait for babylon events to register for spending, it should do this as soon as delegation becomes Active b/c of delays from vigilante/babylon.

Although imo our existing approach won't cause any missed notifications but we can sure make above improvements.

Slack conv (private might not be visible) - https://babylonlabsworkspace.slack.com/archives/D07DYV8DMEK/p1732174227378559