feat: return receipts in data returned by contract calls

[iqdecay]

• Introduce the CallResult struct, that holds the call return in its
  value field, and the receipts in the receipts field.
• This closes issue Improve the data returned by contract calls #35

[iqdecay]

Note: Sometimes some tests are failing but passing when I run them individually, for some weird reason (probably config issue?).

[digorithm]

Note: Sometimes some tests are failing but passing when I run them individually, for some weird reason (probably config issue?).

The tests were designed to be self-contained enough so that state doesn't leak between tests. E.g. we spawn a short-lived fuel-core per test case in harness.rs.

Please provide repro steps if you found this not to be the case. Also, check it against master to see if this was introduced on this branch.

So far I haven't experienced any flakiness in fuels-rs tests, and if that's the case now we have to do the best we can to avoid flakiness in tests.

[iqdecay]

Edit: Issues came from commits of PR #49 , they are not on this branch so the tests run fine now! No flakiness.

[digorithm]

It's looking good! Just a few nits and comments.

[iqdecay]

CI passing as well! 🎉

Made the changes but Github didn't notice

[iqdecay]

Changing docs strings broke CI? wth

[digorithm]

Changing docs strings broke CI? wth

Haha, that's actually what I'm currently investigating. It's failing to compile Sway code when we call forc::build during a test. So weird.

[digorithm]

Good stuff! 😄