feat: IIdempotencyStore – SQLite ADO.NET implementation

[samtrion]

User Story

As a developer using SQLite with Pulse, I want an IIdempotencyStore backed by SQLite, so that I can enforce idempotency in embedded, edge, or test scenarios without requiring a full database server.

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Background

Mirrors the SQL Server (#227) and PostgreSQL (#228) implementations but uses Microsoft.Data.Sqlite and SQLite-specific DDL (TEXT for ISO-8601 timestamps, INSERT OR IGNORE).

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Requirements

• Add src/NetEvolve.Pulse.SQLite/Scripts/002_CreateIdempotencyKeyTable.sql:
  • CREATE TABLE IF NOT EXISTS "{table}" ("IdempotencyKey" TEXT NOT NULL PRIMARY KEY, "CreatedAt" TEXT NOT NULL) using ISO-8601 strings for DateTimeOffset.
• Create SQLiteIdempotencyKeyOptions: ConnectionString, TableName, EnableWalMode, TimeToLive?.
• Implement SQLiteIdempotencyStore : IIdempotencyStore via Microsoft.Data.Sqlite:
  • ExistsAsync: SELECT 1 FROM "..." WHERE "IdempotencyKey" = @key LIMIT 1.
  • StoreAsync: INSERT OR IGNORE INTO "..." VALUES (@key, @createdAt).
• Expose AddSQLiteIdempotencyStore extension overloads in SQLiteIdempotencyMediatorBuilderExtensions.

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Acceptance Criteria

• DDL script creates the table using SQLite syntax and ISO-8601 text columns.
• ExistsAsync returns true for an existing key, false for a new one, and ignores expired keys when TimeToLive is set.
• StoreAsync uses INSERT OR IGNORE and does not throw on duplicates.
• Both AddSQLiteIdempotencyStore overloads register IIdempotencyStore as Scoped.
• Unit tests cover: key exists, key absent, TTL expiry, duplicate insert, options wiring.

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Dependencies

• Requires feat: IIdempotencyStore – EF Core implementation #226 (IdempotencyKeySchema constants).