Fix ICE and type mismatch with array type aliases and const generics

[Dnreikronos]

Summary

• Fix ICE "Const generic not materialized" when type aliases for arrays (e.g. type ArrayU8Len2 = [u8; 2]) are used as struct fields and compared via ==
• extract_type_parameters now extracts const generic length parameters from array types (e.g. N → 2), matching the existing pattern used for Enum/Struct const generics
• MaterializeConstGenerics for TypeId now handles TypeInfo::Alias by recursing into the aliased type, consistent with the existing Ref handling

Test plan

• New e2e test type_alias_array_const_generics covering:
  • Struct fields typed as array aliases
  • Nested array aliases ([ArrayU8Len2; 3])
  • Equality comparison triggering Eq trait const generic path
  • Vec<Alias>::get().unwrap() return type resolution
• All existing type_alias* tests pass (11/11)
• All existing const_generic* tests pass (3/3)
• All existing array* tests pass (18/18)

Closes #7616

[fuel-cla-bot]

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[cursor]

PR Summary

Medium Risk
Touches core type-system const-generic and unification paths in sway-core; scope is narrow but compiler correctness is sensitive.

Overview
Fixes an ICE (Const generic not materialized) and related type mismatches when array type aliases (e.g. type ArrayU8Len2 = [u8; 2]) appear in struct fields, ==, and generic APIs like Vec<Alias>::get().

MaterializeConstGenerics on TypeId now handles TypeInfo::Alias by materializing through the aliased type and re-inserting the alias, mirroring existing Ref behavior.

extract_type_parameters for Array now pairs element types and lengths: when the original length is an ambiguous const-generic name and the concrete side is a literal, it records that binding (same idea as struct/enum const generics).

Adds e2e type_alias_array_const_generics (nested aliases, equality, Vec + unwrap).

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