Update guide: Invoke a contract function in a transaction using SDKs

[briwylde08]

https://developers.stellar.org/docs/build/guides/transactions/invoke-contract-tx-sdk

[ElliotFriend]

Guide was substantively expanded (Rust invoke + test-account examples added late 2025); the JS tab uses the modern contract.Client.deploy/Client.from flow and Java uses current sorobanrpc packages. Closing as completed.