Simplify and Refactor pre_lock_filter

[apfitzge]

Problem

• pre_lock_filter has been unused so far
• want to change from strict filter to allowing different actions to be taken. for example, skip w/o removing it from map

Summary of Changes

• pre_lock_filter takes in transaction state
• pre_lock_filter returns a PreLockFilterAction
• PreLockFilterAction currently only supports simple pass-through

Future Plans

1. Retry throttling

• Add PreLockFilterAction::Skip which allows tx to be skipped, but not removed
• pre_lock_filter will use the current bank slot to compare against a (soon to be introduced) latest retry slot to avoid retrying transactions too often

2. IP filtering

• if IP is sending us enough trash, we can quickly drop the transactions here

Fixes #

[tao-stones]

This could work; I was thinking another possibility of removing both filters to simplify Scheduler. pre_lock_filter could be do before scheduling, pre_graph_filter is bit tricky to determine if belongs to Scheduler. Let's get this moving, while working out details to do filtering early and separately.