Refactor of layout utils

[snejus]

Summary

This PR refactors import-match layout rendering by centralizing layout selection and line generation in beets.util.layout, simplifying the ShowChange display path, and tightening the layout
data model.

What Changed

• Added get_layout_lines() and get_layout_method() in beets.util.layout so layout selection (column vs newline) is handled in one place.
• Replaced Side from a mutable TypedDict with an immutable NamedTuple that exposes derived helpers (rendered, prefix/suffix widths, and rendered width).
• Simplified split_into_lines() from a 3-width tuple API to (first_width, width) and removed legacy last-line empty-string handling.
• Refactored beets.ui.commands.import_/display.py ShowChange to call get_layout_lines() directly and removed duplicate per-class layout-selection logic.
• Updated tracklist width calculation to use Side helpers and explicit width assignment via _replace(width=...).
• Reworked ShowChange tests into snapshot-style assertions for both newline and column layouts, and updated util layout tests to the new split_into_lines() signature.

Why

• Reduces duplicated wrapping/layout logic across UI code paths.
• Makes layout behavior easier to reason about and test at the utility boundary.
• Narrows the display layer to orchestration while keeping transformation/rendering logic in reusable utilities.
• Improves maintainability by moving from loosely typed dict mutation to a typed, self-describing data structure.

[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[snejus]

@JOJ0 this one for you to have a look at!

[codecov]

Codecov Report

❌ Patch coverage is 91.34615% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.73%. Comparing base (05f0ec3) to head (cfc7ffb).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
beets/util/layout.py	89.65%	6 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6442      +/-   ##
==========================================
+ Coverage   69.69%   69.73%   +0.03%     
==========================================
  Files         145      145              
  Lines       18541    18534       -7     
  Branches     3028     3023       -5     
==========================================
+ Hits        12923    12924       +1     
+ Misses       4982     4976       -6     
+ Partials      636      634       -2     

Files with missing lines	Coverage Δ
beets/ui/commands/import_/display.py	82.18% <100.00%> (+0.26%)	⬆️
beets/util/layout.py	83.55% <89.65%> (+4.10%)	⬆️

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[Copilot]

Pull request overview

Refactors import-match layout rendering by replacing TypedDict Side with an immutable NamedTuple, simplifying split_into_lines from a 3-width tuple to two args, and centralizing layout selection logic in beets.util.layout.

Changes:

• Converted Side from TypedDict to NamedTuple with derived helper properties (rendered, prefix_width, etc.) and simplified split_into_lines signature.
• Added get_layout_lines() and cached get_layout_method() in beets.util.layout, removing duplicate layout-selection logic from ShowChange.
• Rewrote ShowChange tests as snapshot-style assertions for both layout modes.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
beets/util/layout.py	Core refactor: Side → NamedTuple, simplified split_into_lines, added get_layout_lines/get_layout_method
beets/ui/commands/import_/display.py	Simplified to use Side constructors and get_layout_lines directly
test/util/test_layout.py	Updated split_into_lines calls to new 2-arg signature
test/ui/commands/test_import.py	Replaced granular tests with snapshot assertions for both layouts

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[snejus]

@JOJ0 added a commit to document Side.