Override RLP decoders with ones from plugins; fix op decoder

[flcl42]

Changes

• Register plugin decoders, allowing to override existing ones
• Add keyed decoders, means in addition to type a string key can be used to retrieve and encoder
• Fix sync trace logs a bit

Types of changes

What types of changes does your code introduce?

• [x] Bugfix (a non-breaking change that fixes an issue)
• [x] New feature (a non-breaking change that adds functionality)
• [x] Breaking change (a change that causes existing functionality not to work as expected)
• [ ] Optimization
• [ ] Refactoring
• [ ] Documentation update
• [ ] Build-related changes
• [ ] Other: Description

Testing

Requires testing

• [ ] Yes
• [x] No

If yes, did you write tests?

• [ ] Yes
• [x] No

Remarks

We need to do the same for tx receipt storage, I guess. But maybe later

[benaadams]

Haha, didn't see was draft :)

[flcl42]

Would be good to have someone from optimism stack review it too.

It's done according to what a learned from @protolambda's answers