Merge std and core libraries

[SwayStar123]

Description

Merges the two libraries. They were initially separate to separate the core logic and fuel vm specific functionality, but that separation is no longer maintained so having a merged library is better.

Closes #6708

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
  • If my change requires substantial documentation changes, I have requested support from the DevRel team
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.

[jjcnn]

Truly a Herculian effort on this one!

I've added a few comments. There shouldn't be much work in them, so there should be time to do them before the release.

The ones about using the reduced std libs can be left for a separate issue if needed.

[jjcnn]

Changing my review status to approved.

The one change that was definitely needed was comments in abi_encoding.rs, which have been added.

My remaining review comments are nits.

[bitzoic]

I would have liked to see more edge cases covered(zero and max values) in the inline tests but these can be added afterward

[kayagokalp]

Tooling side of the things looks good to me. We used to have that if core is not added add it by default and std was opt-out. Now that we remove core we seem to remove the auto core addition thingy as well. Just writing to confirm that this is the desired behaviour.