Support partial sign & marshal binary of partial signed transaction

[0ximalice]

Hi,

I recently added some features to my forked repo and need to contribute back to the origin repo.
All features including

• feat: added PartialSign along with Sign transaction
• fix: new signed signatures are only added on success to prevent unwanted signatures stacking on failed cases (https://github.com/imalic3/solana-go/blob/feature/partial_sign/transaction.go#L397)
• remove a signature verification checked while marshal binary which will be available to marshal partial-signed transaction.
• tests: added partial sign and sign tests

Thanks for your awesome work

[gagliardetto]

Thanks!