Add detailed cycle-breaking comments to topologicallySortTypes

[Copilot]

The cycle-breaking logic in topologicallySortTypes lacked the detailed inline comments present in topologicallySortTables and topologicallySortViews, making it harder for maintainers to understand this critical algorithm.

Changes

• Added comprehensive cycle-breaking strategy comments explaining:

  • Why setting inDegree[next] = 0 is safe (processed map prevents duplicates)
  • How type dependencies differ from table constraints (cannot be added post-creation)
  • PostgreSQL's restrictions on circular type dependencies (only via arrays/indirection)
  • Deterministic ordering via insertion order

• Added explanation for the !processed[neighbor] check that prevents re-adding already-processed types to the queue

Example

The comments now match the structure and detail level of the table sorting function:

// CYCLE BREAKING STRATEGY FOR TYPES:
// Setting inDegree[next] = 0 effectively declares "this type has no remaining dependencies"
// for the purpose of breaking the cycle. This is safe because:
//
// 1. The 'processed' map prevents any type from being added to the result twice, even if
//    its inDegree becomes zero or negative multiple times (see line 344 check).
//
// 2. For circular type dependencies in PostgreSQL, the dependency cycle can only occur
//    through composite types referencing each other. Unlike table foreign keys, type
//    dependencies cannot be added after creation - the entire type definition must be
//    complete at CREATE TYPE time.
//
// 3. PostgreSQL itself prohibits creating types with true circular dependencies
//    (composite type A containing type B, which contains type A) because it would
//    result in infinite size. The only cycles that can occur in practice involve
//    array types or indirection (e.g., A contains B[], B contains A[]), which
//    PostgreSQL allows because arrays don't expand the size infinitely.

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