Consistent type hints in `fork_types.py`

[DistributedDoge]

What was wrong?

Some type annotations in fork_types.py for each fork use bytes type, and some use Bytes alias imported from ..base_types.

fork_types.py

class Transaction:
    ...
    data: Bytes

class Account:
    ...
    code: bytes

class Log:
    ...
    data: bytes

Issue #752 suggests that spec would be more consistent if Bytes alias was applied everywhere to match surrounding code.

This change should not result in any functional difference as Bytes is alias for bytes.

How was it fixed?

For every Log.data and Account.code in src/ethereum/$fork_name/fork_types.py replaced type annotation like so: bytes => Bytes.

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