feat(test-utils): Make MockEthProvider generic over Transaction

[0xOsiris]

Describe the feature

Right now the MockEthProvider fixes T to TransactionSigned making it unusable with OpSignedTransaction.

This could be generic over T:

#[derive(Debug, Clone)]
pub struct MockEthProvider<T = TransactionSigned> {
    /// Local block store
    pub blocks: Arc<Mutex<HashMap<B256, Block<T>>>>,
    /// Local header store
    pub headers: Arc<Mutex<HashMap<B256, Header>>>,
    /// Local account store
    pub accounts: Arc<Mutex<HashMap<Address, ExtendedAccount>>>,
    /// Local chain spec
    pub chain_spec: Arc<ChainSpec>,
    /// Local state roots
    pub state_roots: Arc<Mutex<Vec<B256>>>,
}

This would make the MockEthProvider more extensible to testing in an op-reth stack.

Additional context

No response