Note

Medium Risk
Changes core whitespace/comment emission and import-group layout, which can alter formatted output broadly; risk is mitigated by large idempotent snapshot tests but not zero for edge-case sources.

Overview
Refactors formatter internals so whitespace and comments are modeled as Gap values instead of a Trivia wrapper, and widens several pub(crate) APIs (Layout, Doc, TokenStream, planning types, etc.) for reuse. Shared helpers move onto TokenStream (matching_brace) and token_stream (significant_tokens); Gap gains dangling(), ends_line(), and trivia splitting returns plain gaps (including capping trailing newlines when only inline comments remain).

Emitting now routes through gap_doc / Separator::after so trailing line comments and multiline gaps don’t swallow blank lines between top-level items, fixes inline comment spacing when a gap ends without a following newline, and reworks nested import { … } layout (opening trivia, separators between paths, trailing commas when comments sit before commas, closing-brace line handling).

Adds broad regression coverage for comments (EOF, CRLF, postfix/conditional branches), import sorting/comment ownership, and mixed syntax shapes in a new regressions test module.

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