[Task] Update all Rust examples to use `sandbox` instead of `workspaces`

[gagdiez]

Aprox. two weeks ago they released a new way of testing smart contracts, now we need to update all of our examples

[garikbesson]

Examples:

• "Workspaces -> sandbox" migration near-examples/auctions-tutorial#24
• "Workspaces -> sandbox" migration near-examples/hello-near-examples#51
• "Workspaces -> sandbox" migration near-examples/counters#26
• "Workspaces -> sandbox" migration near-examples/update-migrate-rust#7
• "Workspaces -> sandbox" migration near-examples/guest-book-examples#35
• "Workspaces -> sandbox" migration near-examples/nft-contract-tools#1
• "Workspaces -> sandbox" migration near-examples/ft-contract-tools#1
• "Workspaces -> sandbox" migration near-examples/FT#132
• "Workspaces -> sandbox" migration near-examples/nft-tutorial#74
• "Workspaces -> sandbox" migration near-examples/near-workspaces-examples#1
• "Workspaces -> sandbox" migration near-examples/NFT#232
• "Workspaces -> sandbox" migration near-examples/factory-rust#11
• "Workspaces -> sandbox" migration near-examples/cross-contract-calls#21

Docs:

• Update Integration Tests section docs#2975