Categorize associatedtype declarations as beforeMarks

[Copilot]

associatedtype declarations were categorized as .nestedType, causing organizeDeclarations to sort them after init declarations in protocol bodies. They should be .beforeMarks so they always appear first.

• Split the combined "typealias", "associatedtype" case in DeclarationType.swift so that associatedtype returns .beforeMarks while typealias remains .nestedType.

// Before
case "typealias", "associatedtype":
    return .nestedType

// After
case "typealias":
    return .nestedType

case "associatedtype":
    return .beforeMarks

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.45%. Comparing base (960a338) to head (e6967c6).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2668   +/-   ##
========================================
  Coverage    95.45%   95.45%           
========================================
  Files          178      178           
  Lines        27226    27228    +2     
========================================
+ Hits         25989    25991    +2     
  Misses        1237     1237           

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