fix(abi): handle anonymous events in encodeEventTopics

[Zelys-DFKH]

Summary

Fixes #4461

Root cause

encodeEventTopics in src/utils/abi/encodeEventTopics.ts computes the event signature and prepends it as topic[0] unconditionally. Anonymous events do not include the signature as a topic — the EVM skips it entirely, giving anonymous events four indexed slots instead of three. Because abiItem.anonymous was never checked, encodeEventTopics was producing incorrect topics for any anonymous event.

Fix

Move the signature computation inside a guard and only prepend it for non-anonymous events:

```ts
if (abiItem.anonymous) return topics

const definition = formatAbiItem(abiItem)
const signature = toEventSelector(definition as EventDefinition)
return [signature, ...topics]
```

The return type is loosened from [Hex, ...(Hex | Hex[] | null)[]] to (Hex | Hex[] | null)[] since anonymous events with no args return an empty array.

Tests

Added three unit tests covering anonymous events: no args (returns []), partial args, and all args.

Notes

• Non-anonymous event behaviour is unchanged.
• The signature computation is skipped entirely for anonymous events, not just excluded from the output.

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Latest commit: 19bd5f6

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