refactor(engine): simplify InvalidBlockWitnessHook::on_invalid_block for better testability

[yongkangc]

Current implementation spans 180+ lines handling execution, state collection, proof generation, and witness assembly in a single function.

https://github.com/paradigmxyz/reth/blob/main/crates/engine/invalid-block-hooks/src/witness.rs#L141-L322

Problem:

• Difficult to test individual logic paths without full database setup
• Multiple nested data transformations obscure core witness generation logic

Goal:

• Decompose into smaller functions with clear responsibilities
• Enable testing with mock state providers instead of requiring full StateProviderDatabase
• Each extracted component should be testable with minimal fixture setup

Please add tests for this

[Paulius0112]

@yongkangc can I work on this?

[yongkangc]

@Paulius0112 assigned

[yongkangc]

@0xKarl98 do you wanna work on this?

[0xKarl98]

@yongkangc Yeah ofc i can take it

[yongkangc]

@Paulius0112 had a chat with and will be assigning @0xKarl98

do add some tests to prevent regression as well, thanks!

[yongkangc]

hey @0xKarl98 any updates on this?

[0xKarl98]

Am adding test to it and still on progress