feat(flashtypes): Introduce Minimal Flashtypes Crate

[refcell]

Description

Introduces base-flashtypes, a new crate containing the core primitive types for flashblocks. This extracts Flashblock, Metadata, FlashblockDecodeError, and the execution payload types from rollup-boost-types (which is an unpublished crate we previously depended on) into their own minimal crate.

The main motivation is to remove the rollup-boost dependency from the workspace, and base-reth-flashblocks specifically. By defining these types locally, we avoid pulling in the full rollup-boost crate and its transitive dependencies just for a handful of type definitions. This reduces the dependency tree and gives us more control over flashblocks type wire format.

Eventually, once rollup-boost-types is a published crate, we can deprecate the payload types in base-flashtypes, re-using the types from rollup-boost-types. We could also upstream types from base-flashtypes into rollup-boost-types and deprecate this crate entirely.

Usage

use base_flashtypes::{Flashblock, FlashblocksPayloadV1};

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	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

Approved review 3586033602 from danyalprout is now dismissed due to new commit. Re-request for approval.

[danyalprout]

There are types for this in alloy.

There maybe value in using our own types for this, as it'll be easier for us to add BAL's etc.

cc @haardikk21 for input

[haardikk21]

There are types for this in alloy.

There maybe value in using our own types for this, as it'll be easier for us to add BAL's etc.

cc @haardikk21 for input

We use alloys types for BAL too for the most part. Its the metadata of the FB payload we need to maintain control over. Dont think there's a good way to "modify" a struct to go from a looser typed field in an external crate (serde::Value) to a more stricter typed one so this is fine with me

Approved review 3604818637 from danyalprout is now dismissed due to new commit. Re-request for approval.