feat: migrate database access to async with aiosqlite

[victor1234]

What

Added async database support using aiosqlite and converted the API, services, and DB access layer to fully asynchronous.

Why

Synchronous SQLite access was blocking the FastAPI event loop and limiting concurrency. Async queries allow the server to handle more requests efficiently without blocking I/O.

How

• Add aiosqlite dependency in pyproject.toml and poetry.lock.
• Replace sqlite3 with aiosqlite and introduced an asynccontextmanager for DB connections.
• Convert DB functions (get_book_title, get_book_file_path, get_cover_path, get_authors, etc.) to async.
• Update service functions (generate_*_feed, search_books, etc.) to async and awaited DB calls.
• Make API endpoints (download_book, get_cover, search, root_by_*, etc.) async.
• Update /ready probe to use async DB check.

[Copilot]

Pull Request Overview

This PR converts the OPDS server from synchronous to asynchronous operations by replacing sqlite3 with aiosqlite and making all database-related functions async. The migration enables better concurrent handling of multiple requests and improved performance.

Key changes:

• Migrated from sqlite3 to aiosqlite for async database operations
• Converted all database access functions to async/await pattern
• Updated API endpoints to use async handlers

Reviewed Changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/opds_server/db/access.py	Complete migration from sqlite3 to aiosqlite with async context managers and cursor handling
src/opds_server/services/opds.py	Converted feed generation functions to async and added await calls to database operations
src/opds_server/api/catalog.py	Updated API endpoint handlers to async and added await calls to service functions
src/opds_server/main.py	Updated health check endpoint to use async database connection
pyproject.toml	Added aiosqlite dependency

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[Copilot]

Using async for to iterate over cursor results may not be supported by aiosqlite. Consider using await cursor.fetchall() and then iterating over the results with a regular for loop.

Suggested change

	) as cursor:
	async for book_id, author_id, name in cursor:
	rows = await cursor.fetchall()
	for book_id, author_id, name in rows:

[Copilot]

Using async for to iterate over cursor results may not be supported by aiosqlite. Consider using await cursor.fetchall() and then iterating over the results with a regular for loop.

Suggested change

	) as cursor:
	async for book_id, file_format, filename in cursor:
	rows = await cursor.fetchall()
	for book_id, file_format, filename in rows: