feat: IIdempotencyStore – PostgreSQL ADO.NET implementation

[samtrion]

User Story

As a developer using PostgreSQL with Pulse, I want an IIdempotencyStore backed by PostgreSQL ADO.NET, so that I can enforce idempotency in applications that use NetEvolve.Pulse.PostgreSql without adopting EF Core.

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Background

Mirrors the SQL Server implementation (#227) but uses Npgsql and PostgreSQL-specific DDL (TIMESTAMP WITH TIME ZONE, ON CONFLICT DO NOTHING).

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Requirements

• Add src/NetEvolve.Pulse.PostgreSql/Scripts/IdempotencyKey.sql:
  • Table "{schema}"."IdempotencyKey" with idempotency_key VARCHAR(500) NOT NULL PRIMARY KEY and created_at TIMESTAMP WITH TIME ZONE NOT NULL.
  • PostgreSQL functions: fn_exists_idempotency_key, fn_insert_idempotency_key, fn_delete_expired_idempotency_keys.
• Create PostgreSqlIdempotencyKeyOptions: Schema, TableName, TimeToLive?.
• Implement PostgreSqlIdempotencyStore : IIdempotencyStore via Npgsql ADO.NET:
  • ExistsAsync: calls fn_exists_idempotency_key.
  • StoreAsync: calls fn_insert_idempotency_key; ignores PostgreSQL error 23505 (unique violation).
• Expose AddPostgreSqlIdempotencyStore extension overloads in PostgreSqlIdempotencyMediatorBuilderExtensions.

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Acceptance Criteria

• DDL script creates the table and all three functions using PostgreSQL syntax.
• ExistsAsync returns true for an existing key, false for a new one, and ignores expired keys when TimeToLive is set.
• StoreAsync does not throw on error 23505.
• Both AddPostgreSqlIdempotencyStore overloads register IIdempotencyStore as Scoped.
• Unit tests cover: key exists, key absent, TTL expiry, duplicate insert, options wiring.
• Integration tests cover

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Dependencies

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