Enforce setting "sender" (instead of emitting a console WARN)

[andreibancioiu]

• https://github.com/multiversx/mx-sdk-js-core/blob/main/src/compatibility.ts#L12
• Exceptions can be thrown for non-Mainnet transactions

[andreibancioiu]

For legacy approaches of constructing transactions, we will still be emitting WARNs, instead of throwing errors:

• https://github.com/multiversx/mx-sdk-js-core/pull/421

However, the new transaction factories of v13 do require the sender parameter:

• https://docs.multiversx.com/sdk-and-tools/sdk-js/sdk-js-cookbook-v13