feat: separate flashblocks extension crate

[meyer9]

• Moves flashblock extension to base-flashblocks-node crate. Configuration stays in flashblock lib crate.
• Updates node to depend on flashblocks-node instead

This allows base-client-engine to depend on flashblocks state and also inject the engine into addons in the flashblock extension. Previously, this would have caused an import cycle.

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 2/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2

[meyer9]

oh maybe we can move test harness, benches, and tests back to the original crate... fixed

[meyer9]

Will wait for 2 reviews to merge since this is a crate reorganization

[refcell]

This works, can always rename later!