typing: add missing types to beets.importer

[snejus]

• This change tightens typing across the importer pipeline, mainly in beets.importer.session, beets.importer.stages, beets.importer.tasks, beets.importer.state, and beets.util.pipeline.

• Architecturally, it makes the importer's core flow more explicit:

  • session methods now declare clear input/output types
  • pipeline stage message types are named and propagated through Pipeline
  • task classes expose more precise return values and argument types
  • plugin event dispatch for import_task_created now has a typed contract

• A small but important part of the change is switching importer config handling to work with confuse views more safely, using .set(...) and .get(...) instead of replacing values directly. This keeps config mutation aligned with the config system instead of treating it like a plain dict.

• There are also a few correctness-oriented fixes uncovered while adding types, such as:

  • keeping byte/string path handling consistent in importer task cleanup and archive extraction
  • making nullable values explicit before use
  • returning None in places that already behaved that way implicitly

• High-level impact: no feature change to importer behavior is intended. The main benefit is a clearer, more strongly typed importer architecture that is easier to reason about, safer to refactor, and better at catching edge cases during development.

[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.

[codecov]

Codecov Report

❌ Patch coverage is 95.65217% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.58%. Comparing base (d179dbb) to head (9ffe742).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
beets/importer/tasks.py	92.53%	4 Missing and 1 partial ⚠️
beets/util/pipeline.py	95.23%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6711   +/-   ##
=======================================
  Coverage   75.57%   75.58%           
=======================================
  Files         162      162           
  Lines       20806    20815    +9     
  Branches     3292     3291    -1     
=======================================
+ Hits        15725    15733    +8     
- Misses       4306     4307    +1     
  Partials      775      775           

Files with missing lines	Coverage Δ
beets/dbcore/db.py	94.06% <100.00%> (-0.03%)	⬇️
beets/importer/session.py	94.32% <100.00%> (-0.04%)	⬇️
beets/importer/stages.py	88.62% <100.00%> (-0.14%)	⬇️
beets/importer/state.py	91.37% <100.00%> (+0.15%)	⬆️
beets/plugins.py	88.84% <100.00%> (ø)
beetsplug/convert.py	74.70% <100.00%> (-0.08%)	⬇️
beetsplug/fetchart.py	74.07% <100.00%> (ø)
beets/util/pipeline.py	91.96% <95.23%> (-0.34%)	⬇️
beets/importer/tasks.py	91.32% <92.53%> (+0.18%)	⬆️

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[Copilot]

Pull request overview

grug see PR try make importer more typed. goal good: less guess, more clear pipe flow. but grug also see one bug where plugin return shape now break old contract.

Changes:

• add many type hints across importer tasks/session/stages, and pipeline typing
• make importer config mutation use confuse .set(...) / .get(...)
• small cleanup in plugins event typing and some path bytes handling

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
beetsplug/fetchart.py	guard prune call when candidate path maybe None
beetsplug/convert.py	small pipeline call simplification
beets/util/pipeline.py	add typing + generic Pipeline shape + adjust parallel run structure
beets/plugins.py	add overload for typed send() event contract
beets/importer/tasks.py	add types, safer config access, adjust archive extract bytes handling, and change import_task_created dispatch path
beets/importer/state.py	add types for ImportState and context manager methods
beets/importer/stages.py	add stage message type aliases and stage function return types
beets/importer/session.py	add types + switch config mutation to confuse .set(...) / .get(...)
beets/dbcore/db.py	make LazyConvertDict implement Mapping for typing
.git-blame-ignore-revs	ignore rev for this typing-only-ish change set