Fix SROA miscompilation issues

[ironcev]

Description

This PR fixes two miscompilation issues in SROA:

• GEP pointers coming through block arguments were treated in combine_indices as having a known source access at index 0 (returning empty vector for indices). This is obviously wrong since at run-time the argument can come from any of the predecessor and have an arbitrary, predecessor dependent value.
• The case of combine_indices returning None and signaling that the source of indices was unknown, wasn't inspected when removing symbols from potential candidates.

The provided tests cover both issues and will fail if any of them regresses.

Fixing these two issues didn't cause any changes in o2 trade-account benchmarks. In some o2 order-book benchmarks there are slight regressions ~0.04% in average and 0.05% max.

Additionally the PR removes reduntant forc build run from the attributes_error_type_and_error test.

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.

[cursor]

PR Summary

Medium Risk
Changes optimizer correctness logic in release builds; wrong handling would miscompile memory accesses, though regressions are covered by new tests and benchmarks reportedly show only minor impact.

Overview
Fixes release-mode SROA miscompiles when aggregate locals are accessed through pointers that reach a join block as non-entry block arguments (e.g. &t.1 vs &t.2 merged in an if).

combine_indices no longer treats every block argument as offset zero: only entry block args (function parameters) contribute no indices; join block args now return None because the pointer offset depends on the predecessor.

SROA candidate filtering now drops locals when combine_indices is None, so aggregates are not scalarised when loads/stores go through those unknown-offset pointers.

Adds Block::is_entry, IR verifier rules that the entry block is named entry (and no other block uses that name), plus IR and e2e regression tests. Trims a duplicate forc build in an unrelated fail-test snapshot.

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[ironcev]

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