fix: tests removing ROCOCO contracts

[AlexD10S]

This PR addresses issues with failing tests when run locally due to dependencies on the now-inactive ROCOCO Contracts parachain.

Changes

• Replaced the endpoint for the ROCOCO Contracts parachain with a stable testnet supporting pallet_contracts: wss://rococo-contracts-rpc.polkadot.io → now using Pop Network
• Removed messaging and defaults referencing ROCOCO_CONTRACTS as the default chain.
• Upgraded Yarn to a newer version to resolve issues encountered during local test runs.
• The CI jobs: ui-chrome-tests and ui-firefox-tests were failing too: https://github.com/use-ink/contracts-ui/actions/runs/15389251564. Fixed updating cypress and cypress.config.ts

Steps to run tests locally:

1. Start a local contracts node: https://github.com/use-ink/substrate-contracts-node?tab=readme-ov-file#usage
2. yarn
3. yarn start

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[cmichi]

Nice!