refactor: Replace ckb-standalone-types with ckb-gen-types

[EthanYuan]

Since ckb-gen-types (which supports no-std) has been separated from ckb-types, it's possible to replace ckb-standalone-types with it. This refactoring makes future maintenance more consistent.

This refactoring is essentially painless, requiring only minor modifications to the Cargo.toml file.

[xcshuan]

There are some methods that do not exist in ckb-gen-types, such as converting Byte32 to [u8;32] through unpack.

[EthanYuan]

There are some methods that do not exist in ckb-gen-types, such as converting Byte32 to [u8;32] through unpack.

Indeed ckb-standalone-types has some forks. I'll check again to add those to ckb-gen-types.
Thanks for pointing that out.

[quake]

There are some methods that do not exist in ckb-gen-types, such as converting Byte32 to [u8;32] through unpack.

we are going to merge this PR: nervosnetwork/molecule#80

you may use into instead of unpack after a new release version of molecule is out.

foo.byte32([u8; 32].into())