feat: enhance clone api

[twoeths]

Motivation

• when upgrading BeaconState, we have to manually clone() each field of ExecutionPayloadHeader from bellatrix -> capella and capella->deneb

Description

• enhance clone() api to accept a pointer to super-set type
• this is comptime check so should be safe
• list of types are applied: Container, List, Vector

[gemini-code-assist]

Summary of Changes

Hello @twoeths, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a powerful enhancement to the clone API for SSZ (Simple Serialize) Container, List, and Vector types. By allowing the clone function to accept a pointer to any type (anytype) as its output, it facilitates seamless data migration from a source type to a destination type that is a superset of the source. This feature is particularly beneficial for managing evolving data structures, such as those encountered during Ethereum beacon state upgrades (e.g., Bellatrix to Capella, Capella to Deneb), where fields are added over time. The change reduces manual field-by-field assignments, making the code cleaner, more maintainable, and less prone to errors, all while maintaining compile-time type safety.

Highlights

• Enhanced clone API: The clone functions for Container, List, and Vector types now accept anytype as the output parameter, enabling cloning into a superset type.
• Compile-time Safety: This enhancement is designed with compile-time checks, ensuring type safety when cloning between compatible (superset) structures.
• Simplified State Upgrades: The new API significantly reduces boilerplate code in state transition logic, as demonstrated by refactoring upgradeStateToCapella and upgradeStateToDeneb to use the enhanced clone for ExecutionPayloadHeader.
• Improved Test Coverage: New test cases have been added for FixedContainerType, VariableContainerType, FixedListType, VariableListType, FixedVectorType, and VariableVectorType to validate cloning into larger, compatible types.

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[gemini-code-assist]

Code Review

This pull request introduces a significant enhancement to the clone API for SSZ types (Container, List, Vector), allowing cloning into a superset type. This is a well-executed improvement that greatly simplifies the state upgrade logic, as demonstrated by the refactoring in upgrade_state_to_capella.zig and upgrade_state_to_deneb.zig. The use of anytype and compile-time checks is idiomatic and effective. The accompanying tests are thorough and validate the new functionality well. My review comments focus on further improving safety by adding comptime assertions to the new clone functions, in accordance with the repository's style guide, which emphasizes the rigorous use of assertions.

[twoeths]

applied the new clone() api here and the below upgrade_state_to_deneb.zig

[spiral-ladder]

amazing!

[spiral-ladder]

LGTM with nits

[spiral-ladder]

committed my nitpicks; LGTM