Add initial support for trait constraints

[tritao]

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So this is the initial work for trait contraints and is still not ready for review.

The final PR will actually be split up since this one also contains a fix for https://github.com/FuelLabs/sway/issues/2786.

Sending this as a draft so @emilyaherbert can take a look at an issue that came up: https://github.com/FuelLabs/sway/issues/2838

[mohammadfawaz]

The final PR will actually be split up since this one also contains a fix for https://github.com/FuelLabs/sway/issues/2786.

So a fix for #2786 will be made in a separate PR? That's good! We like incremental PRs :)

So this is the initial work for trait constraints and is still not ready for review.

Are we ready for this or are we planning on closing out all the declaration engine work before finishing trait constraints? It would be nice if all the DE tasks were completed before attempting trait constraints in case there are any surprises in those remaining tasks.

[tritao]

Rebased

[tritao]

Closing since this work is being picked up by @emilyaherbert