Replace Janus queue with asyncio.Future

[simonw]

Closes:

• Research if I can drop Janus #1752

AI generated patch explanation: https://gisthost.github.io/?e2b8d9c7666e988b5c003ff5e5ef3098

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📚 Documentation preview 📚: https://datasette--2715.org.readthedocs.build/en/2715/

[codecov]

Codecov Report

❌ Patch coverage is 0% with 50 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (46d90a0) to head (2e1fed0).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
datasette/database.py	0.00%	50 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2715   +/-   ##
=====================================
  Coverage   0.00%   0.00%           
=====================================
  Files         57      57           
  Lines       8763    8776   +13     
=====================================
- Misses      8763    8776   +13     

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[simonw]

Note that even though we dropped the Janus queue we still queue writes using a standard library Queue, which is created here:

datasette/datasette/database.py

Lines 379 to 383 in 46d90a0

	async def _send_to_write_thread(
	self, fn, block=True, isolated_connection=False, transaction=True
	):
	if self._write_queue is None:
	self._write_queue = queue.Queue()

[simonw]

From the coverage report it looks like our tests don't exercise the various cases where an exception is raised during a query.