feat: typed deserialization

[gagdiez]

Currently the outter deserialization returns a DecodeType that we expect users to cast to their own type T. This change modifies the interface from deserialize(...): DecodeType to an automatic casting deserialize<T>(...): T.

For JS users this makes no difference, since there are no types involved anyway.

For TS users this is a breaking change, since deserialize will now return an unknown type instead of a DecodeType by default if no T is given. However, we would expect users to always be want to cast to T.

Note: This does not change the internal logic of the library, which keeps using DecodeType to maintain consistency.

Before:

const decoded_A = deserialize(...)                     // decoded type is borsh.DecodedType
const decoded_B = <MyClass> deserialize(...) // decoded type is MyClass

Now

const decoded_A =  deserialize(...)                    // decoded type is unknown
const decoded_B =  deserialize<MyClass>(...) // decoded type is MyClass