feat(flashtypes): Add validation utilities, Metadata helpers, and Fla…

[AdekunleBamz]

Summary

This PR enhances the base-flashtypes crate with validation utilities, helper methods, and comprehensive unit tests to improve developer experience and code reusability.

Changes

New validation module

Added common validation functions for flashblock data:

• is_non_zero_address() - validate non-zero addresses
• is_valid_state_root() / is_valid_block_hash() - validate non-zero hashes
• is_valid_blob_gas() - validate optional blob gas values
• is_valid_gas_usage() - validate gas used vs limit
• is_valid_timestamp() - validate non-zero timestamps
• is_valid_transaction_bytes() - validate non-empty transaction data

Metadata helper methods

• is_empty() - check if metadata has no receipts or balance updates
• receipts_len() / balance_updates_len() - count tracked items
• balance_for() - lookup balance by address
• has_balance_update() - check if address has pending update

Flashblock convenience methods

• has_base_payload() - check if base payload is present
• is_first_chunk() - check if this is index 0
• transaction_count() - get number of transactions
• has_withdrawals() - check for withdrawal presence

Tests

• Added unit tests for all new validation functions
• Added unit tests for Metadata helper methods
• Added unit tests for Flashblock convenience methods

Motivation

These utilities reduce boilerplate when working with flashblock types and provide a consistent API for common validation patterns used throughout the codebase.

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	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

[AdekunleBamz]

@meyer9, Can you please tell me why this was closed?