Remove unsafe code from macro expansions

[nbaksalyar]

Motivation

• The sol! macro cannot be used in projects with strict unsafe code policies.
• The current unsafe implementation of abi_decode_raw is not efficient: binary search (O(log n)) is slower than a simple jump table (O(1) or O(n) at worst, for e.g. compare the MIR/asm output).

Solution

• Switch abi_decode_raw to use a constant jump table instead of a runtime binary search.
• Generate safe code to convert between enum variants and u8 statically.
• Make the as_u8 function constant.
• Additionally, allow clippy::empty_structs_with_brackets in the generated code.

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

[DaniPopes]

The current unsafe implementation of abi_decode_raw is not efficient: binary search (O(log n)) is slower than a simple jump table (O(1) or O(n) at worst, for e.g. compare the MIR/asm output).

This is not true, I would recommend you compare the LLVM IR and/or assembly output for a large calls enum, for example Foundry's Vm. The binary search gets unrolled, made branchless and constant-time at compile-time, while the switch gets codegen'd as a binary search regardless because all the match arms have different code sizes.

In this case we can just remove the get_unchecked because the optimizer knows that the returned index is guaranteed to be in-bounds.

The other changes are fine.

[nbaksalyar]

Thank you!