feat: support permit2 on superchainweth

[0xDiscotech]

Description

Permit2 functionality added to the SuperchainWETH contract.

Changes made to WETH98 to support this:

• Updated the visibility of the allowance mapping to internal and created a public getter.
• Updated the visibility of the balanceOf mapping to internal and created a public getter for consistency.

In SuperchainWETH:

• Override the allowance getter to return the maximum allowance when using Permit2.

Tests

New unit tests to cover the Permit2 integration with SuperchainWETH.

Additional context

The SuperchainWETH contract inherits from WETH98, which has allowance as a public mapping, making it non-overridable. Our approach was to follow OpenZeppelin's pattern by renaming allowance to _allowance and making it an internal state variable. This allowed us to add an allowance getter and make it virtual, enabling easy overriding. Some logic in this contract, as well as in DelayedWETH, had to be modified accordingly.
The change in balanceOf is only for consistency to follow the allowance pattern.

Metadata

#11899

[mslipper]

/ci authorize 5224eb9

[tynes]

Looks like a flake:

    sequencer_failover_setup.go:84: 
                Error Trace:    /var/opt/circleci/data/workdir/op-e2e/system/conductor/sequencer_failover_setup.go:84
                                                        /var/opt/circleci/data/workdir/op-e2e/system/conductor/sequencer_failover_test.go:19
                Error:          Received unexpected error:
                                leadership lost while committing log
                Test:           TestSequencerFailover_SetupCluster