fix(docs): Fix event type definitions to use H160 for ink! v6 compatibility

[CECILIA-MULANDI]

Summary

Corrects the Events documentation to use H160 type for account addresses, resolving type mismatch errors when developers follow the examples in ink! v6.

Problem

The current documentation shows event definitions using AccountId:

#[ink(event)]
pub struct Transferred {
    from: Option<AccountId>,  // Causes compilation error
    to: Option<AccountId>,
    value: Balance,
}

When developers follow this example with ink! v6, they encounter a type mismatch error:

error[E0308]: mismatched types
expected `AccountId`, found `H160`

This occurs because Self::env().caller() returns H160 in ink! v6's default environment (pallet-revive), not AccountId.

Changes Made

Event Type Definitions

• Changed Option<AccountId> to Option<H160> in all event examples
• Updated signature topic example from blake2b("Transferred(Option<AccountId>,Option<AccountId>,u128)") to blake2b("Transferred(Option<H160>,Option<H160>,u128)")
• Ensured consistency across all code snippets in the Events documentation

Files Modified

• docs/basics/events.md

Why H160 in ink! v6?

ink! v6 migrated from pallet-contracts to pallet-revive, which prioritizes Ethereum/Solidity compatibility:

• pallet-revive uses H160 (20-byte addresses) instead of traditional 32-byte AccountId for Ethereum compatibility
• Address is a type alias for H160 in ink_primitives (both are interchangeable)
• Enables compatibility with Ethereum tooling like MetaMask, Hardhat, and Solidity contracts
• Self::env().caller() now returns H160 by default

Verification

Matches official example: The official ERC20 example uses Address (alias for H160)

Compiles successfully: Code examples now compile without type mismatch errors in ink! v6

Consistent with pallet-revive: Aligns with pallet-revive's H160 address type

References

• pallet-revive documentation
• Official ERC20 example using Address which is a type alias for H160

Testing

• Tested code examples locally with ink! v6
• Verified examples compile without errors
• Cross-referenced with official ink-examples like the ERC20 example in the repository