Less stateful RawTransaction

[dahlia]

Context:

Maybe it's better to change the type of RawTransaction.Actions... 😕

Currently RawTransaction consists of many mutable types like byte[] and Dictionary<K, V>. If we want RawTransaction to be freer from state I believe we need to adjust other fields too. Seems like it should be a separated patch.

[longfin]

In Libplanet/Tx/RawTransaction.cs

        public long Nonce { get; }

        public byte[] Signer { get; }

        public byte[] PublicKey { get; }

        public byte[][] UpdatedAddresses { get; }

        public string Timestamp { get; }

        public byte[] Signature { get; }

        public IEnumerable<IDictionary<string, object>> Actions { get; }

• byte[] → ImmutableArray<byte>
• IEnumerable<IDictionary<string, object>> → IEnumerable<IImmutableDictionary<string, object>>

[minhoryang]

I'll handle this.