add Unknown transaction variant

[hal3e]

FuelLabs/fuels-rs#1477

BREAKING: Added Unknown transaction variant.

Checklist

• Breaking changes are clearly marked as such in the PR description and changelog
• New behavior is reflected in tests
• If performance characteristic of an instruction change, update gas costs as well or make a follow-up PR for that
• The specification matches the implemented behavior (link update PR if changes are needed)

Before requesting review

• I have reviewed the code myself
• I have created follow-up issues caused by this PR and linked them here

After merging, notify other teams

[Add or remove entries as needed]

• Rust SDK
• Sway compiler
• Platform documentation (for out-of-organization contributors, the person merging the PR will do this)
• Someone else?

[xgreenx]

This kind of change should be done differently. From the protocol level, we don't have unknown transactions since it is impossible to do a state transition if the transaction is unknown.

A new variant should be handled by the code that may receive a new variant of the enum. Maybe you want to look into fuel-core-client since it is where you fetch transactions from the GraphQL.

[hal3e]

Thanks for the clarification.