Make treasury interface closer to ton library wallet interface

[talkol]

Is your feature request related to a problem? Please describe.
When porting code from ton library, I usually send with value as string:

await walletContract.sendTransfer({
    secretKey: key.secretKey,
    seqno: seqno,
    messages: [
      internal({
        to: "EQDrjaLahLkMB-hMCmkzOyBuHJ139ZUYmPHu6RRBKnbdLIYI",
        value: "0.001", // 0.001 TON
        body: "Hello", // optional comment
        bounce: false,
      })
    ]
  });

Describe the solution you'd like
Right now all of the treasury send interfaces accept only bigint, let's make them similar to accept string too and do toNano automatically like ton wallets

[IAlexandrl]