bpd plugin: use asyncio directly and remove bluelet

[snejus]

So I was looking to add types to beets.util.bluelet and realised that it is only used by BPD plugin. Instead of investing any time into it, I scrapped it and used asyncio directly in BPD. I used GitHub search to check that it is not used outside of our codebase.

---

• Replaces the custom coroutine scheduler in beets.util.bluelet with Python's built-in asyncio for the bpd plugin.

• In beetsplug/bpd/__init__.py, the server architecture shifts from Bluelet generators and event objects to native async I/O:

  • connection handling now uses asyncio.start_server
  • connection flows are rewritten as async def methods with await
  • notification delivery is handled with background asyncio tasks
  • socket lifecycle and disconnect handling move to asyncio stream readers/writers

• This removes an internal async framework from the codebase, consolidates bpd on a standard runtime model, and makes the networking layer simpler to reason about and maintain.

• Tests in test/plugins/test_bpd.py are updated to mock asyncio.start_server instead of Bluelet internals, matching the new server entrypoint and preserving coverage around dynamic port assignment.

[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.

[Copilot]

Pull request overview

grug see PR move bpd plugin off custom Bluelet scheduler and onto stdlib asyncio. this remove homegrown async engine and make server code speak native async/await.

Changes:

• rewrite beetsplug.bpd server + connection flow to asyncio.start_server and stream reader/writer
• remove beets.util.bluelet module
• update BPD tests + changelog for new server entrypoint and behavior

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
beetsplug/bpd/__init__.py	replace Bluelet generator scheduler with asyncio servers/tasks; refactor connection I/O to streams
beets/util/bluelet.py	delete Bluelet implementation (no longer used)
test/plugins/test_bpd.py	mock asyncio.start_server instead of Bluelet listener for dynamic port assignment test
docs/changelog.rst	add unreleased changelog entry noting BPD move to asyncio

[codecov]

Codecov Report

❌ Patch coverage is 77.90698% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.87%. Comparing base (74c2d98) to head (35579c4).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
beetsplug/bpd/__init__.py	77.90%	17 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6903      +/-   ##
==========================================
+ Coverage   75.69%   75.87%   +0.17%     
==========================================
  Files         163      162       -1     
  Lines       21412    21107     -305     
  Branches     3384     3336      -48     
==========================================
- Hits        16208    16015     -193     
+ Misses       4405     4309      -96     
+ Partials      799      783      -16     

Files with missing lines	Coverage Δ
beetsplug/bpd/__init__.py	75.90% <77.90%> (+0.14%)	⬆️

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