fix(flashblocks): ensure flashblocks exex does not lag

[danyalprout]

Descrption

Approximately every 6 minutes our nodes that have Flashblock enabled print out a warning regarding the WAL containing too many blocks.

I opened a small diff to Reth and deployed this. Confirmed this is related to the flashblocks-exex.

Some(("flashblocks-canon", NumHash { number: 40471100, hash: 0x35054e96ee1f8c86d03344f36d25fab802108d1f32bc7fbb8aced5585bc23ae9 }))

The lag seems to be ~400 blocks behind every time. We should ensure this is either expected (maybe due to safe head updates or something) or fix.

[danyalprout]

Looked into this with @refcell, there are two things happening here:

1. The Reth library always stores up to finalized block (which on Base can be over the 128 block warning threshold).
2. For both crates where we currently use ExEx's (flashblocks and tracex), we don't actually need them and can just use a direct canonical block subscription

For 1) we're going to make the warning depth configurable so it doesn't warn on rollups and for 2) we'll migrate away from the ExEx framework for our current code.

[danyalprout]

Reth changes here: paradigmxyz/reth#20867

[refcell]

Reth changes here: #316

Thanks for linking!