Add runtime feature set

[ChihChengLiang]

Describe the feature you would like

The Scroll's and Taiko's forks have diverged significantly from this codebase. The cause for the divergence is our codebase has some L1-specific features, and the collaborating teams need to customize for L2 use cases.

We plan to increase the modularity of the codebase so that we can minimize the difference between different forks.

A while ago @Brechtpd proposed the idea of having runtime configs. Teams can include the features they want by configuring the feature set.

@ed255 proposed that we introduce a feature set that looks like

enum FeatureSet {
  EthereumL1,
  Scroll,
  Taiko,
}

However, the team-specific flag might be confusing because it doesn't convey what are the functionalities to include and why they are included. For example, Scroll skips TestBalanceOverflow and TestDifficulty in Ethereum tests. But it is hard to expect those tests to be skipped by seeing a feature named "scroll". When we see tests are skipped with if match!(feature_set, FeatureSet::Scroll), it is hard to guess why they are skipped.

I propose we name the FeatureSet with its functionalities.

enum FeatureSet {
  EthereumL1,
  ZeroDifficulty,
  L2Balance,
}

And we define variables to include those features.

const ScrollFeatures = [ZeroDifficulty, L2Balance]

if match!(feature_set, FeatureSet::ZeroDifficulty) would tell the exact reason why a test is skipped.

Additional context

Before we work on an actual PR, we need some input on these.

• What feature flags should we include?
• How do we structure the flags? What module should we put the feature set in and where to configure them?

[Brechtpd]

Feature set with specific features sounds good to me!

On the Taiko side I can think of these features:

• No fee payment for 1st transaction. The 1st transaction in Taiko is a generated transaction to help sync data between L1 and L2. It also does some additional checks so we don't have to do them directly in a circuit. Maybe in the future this will a be a dedicated transaction type though.
• Disable standard EIP-1559 calculation to calculate the basefee
• Invalid tx support

I think that's it, will add later if there are more.