This commit refactors the Address struct and its methods to improve
its functionality and usability.The AddressInner struct now holds
the payload and network, and the PhantomData<V> type is used to track
the network validation state.
Also as_unchecked and assume_checked_red methods are added to allow
conversion between checked and unchecked network validation state.
Signed-off-by: Harshil Jani <harshiljani2002@gmail.com>
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