Cost of contract calls snapshot tests

[xunilrj]

Description

This PR is a prequel for #7419.
It will set the baseline, which future PRs need to improve.

Apart from that it also:
1 - Fix a problem with SubtsType for TyConstantDecl;
2 - Introduce a new way to write snapshot tests. Now the test source code can have "blocks"

    /* START BOOL */
    fn in_bool(v: bool) -> bool;
    /* END BOOL */

These blocks can be manipulated from inside the snapshot.toml. In this case, the toml is:

cmds = [
    "forc test --path {root} --release --experimental const_generics",
    { repeat = "for-each-block", cmds = [
        "forc test --path {root} --release --experimental const_generics"
    ] }
]

Which repeats the inner forc test for each block, removing all others. That allows me to check the cost of the contract method selection algorithm for each contract method.

For example, cost_of_in_array_64 with all other contract methods costs 60382, but alone it only costs 58218, which means that around 2000 was "wasted" in the contract method selection.

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.

[codspeed-hq]

CodSpeed Performance Report

Merging #7440 will not alter performance

_{Comparing xunilrj/cost-of-contract-calls (3be5de3) with master (97efa22)}

Summary

✅ 25 untouched

[ironcev]

Very useful extensions of our snapshot testing infrastructure! ❤️ Both the blocks and also getting the historical gas values in HTML. Excellent documentation as well! We definitely need it considering how feature-rich snapshot testing becomes.