Implement SQLite-based `KvStore` implementation

[dahlia]

Background

To support the migration from Deno KV to SQLite in our tutorials (see #272 and #273), we need a SQLite-based implementation of the KvStore interface.

This implementation would enable users to use SQLite as their persistent storage backend while maintaining compatibility with Fedify's existing KvStore API.

Proposed Implementation

Create a SqliteKvStore class that implements the KvStore interface using SQLite as the underlying storage mechanism.

Key Requirements

• Cross-runtime compatibility: Support Node.js (node:sqlite), Deno (node:sqlite compatible), and Bun (bun:sqlite)
• API compatibility: Full implementation of the existing KvStore interface
• Performance: Efficient SQLite operations with proper indexing
• Reliability: Proper error handling and transaction support
• Type safety: Full TypeScript support with proper type definitions

Packaging Options

Two potential approaches for distribution:

1. Integrated approach: @fedify/fedify/x/sqlite

   • Pros: Easier discovery, single dependency
   • Cons: Increases main package size

2. Separate package: @fedify/sqlite

   • Pros: Optional dependency, cleaner separation of concerns
   • Cons: Additional package to maintain, potential version sync issues

Implementation Details

• Use native SQLite modules across all supported runtimes
• Implement proper schema migration handling
• Support for TTL (time-to-live) functionality if needed
• Comprehensive test coverage across all target runtimes
• Clear documentation and usage examples

Benefits

1. Tutorial modernization: Enables migration away from Deno KV in tutorials
2. Production readiness: Provides a solid SQLite option for production use
3. Developer experience: Familiar SQLite database with KvStore convenience
4. Cross-platform: Works consistently across Node.js, Deno, and Bun

Acceptance Criteria

• SqliteKvStore class implements full KvStore interface
• Works with Node.js v22+ using node:sqlite
• Works with Deno v2.2+ using node:sqlite compatible module
• Works with Bun using bun:sqlite
• Comprehensive test suite covering all runtimes
• Documentation and usage examples
• Decision made on packaging approach (@fedify/fedify/x/sqlite vs @fedify/sqlite)

[notJoon]

seems related with #2

[nyeong]

I'll take this issue if it's not time-sensitive. I have no experience in Deno and Bun, so maybe I need some time... 👀

[dahlia]

@nyeong No hurries, go for it!

[nyeong]

Do we have plans for additional modules that depend on SQLite? If not, I think an integrated approach is a more sound choice, since there would be no extra dependencies, thanks to native SQLite modules, available in each runtime environment.