feat: PostgreSQL ADO.NET implementation of IIdempotencyStore

[Copilot]

Adds a PostgreSQL-native IIdempotencyKeyRepository backed by Npgsql ADO.NET, mirroring the existing SQL Server implementation without requiring EF Core.

DDL (Scripts/IdempotencyKey.sql)

• Table IdempotencyKey with idempotency_key VARCHAR(500) PK and created_at TIMESTAMP WITH TIME ZONE
• fn_exists_idempotency_key(key, valid_from?) — TTL-aware existence check
• fn_insert_idempotency_key(key, created_at) — INSERT … ON CONFLICT DO NOTHING
• fn_delete_expired_idempotency_keys(valid_from) — cleanup helper

Implementation

• PostgreSqlIdempotencyKeyRepository (internal sealed) — calls the above functions via NpgsqlCommand; catches PostgresException with SqlState == "23505" in StoreAsync as a safety net
• PostgreSqlIdempotencyMediatorBuilderExtensions — three AddPostgreSqlIdempotencyStore overloads (connection string, factory, options action) registering IIdempotencyKeyRepository as Scoped

Usage

services.AddPulse(config => config
    .AddPostgreSqlIdempotencyStore(
        "Host=localhost;Database=MyDb;Username=postgres;******;",
        opts => opts.TimeToLive = TimeSpan.FromHours(24)
    )
);

Tests

• Constructor validation tests for PostgreSqlIdempotencyKeyRepository
• DI registration tests for all three extension overloads (service types, lifetimes, options wiring)
• Integration tests (PostgreSqlAdoNetIdempotencyTests) running against a real PostgreSQL container via Testcontainers, covering: key absent, key present, different key, multiple keys, duplicate insert (same scope), cross-scope duplicate insert (exercises the 23505 catch path), TTL within range, and TTL expired scenarios

[samtrion]

@copilot Add also Integration tests

[Copilot]

@copilot Add also Integration tests

Added in f9e0cdd:

• PostgreSqlAdoNetIdempotencyInitializer — reads Scripts/IdempotencyKey.sql, substitutes :schema_name/:table_name placeholders (same approach as the outbox initializer), and wires up AddPostgreSqlIdempotencyStore
• PostgreSqlAdoNetIdempotencyTests — inherits all 8 scenarios from IdempotencyTestsBase (key absent, key present, different key, multiple keys, duplicate insert, cross-scope duplicate, TTL within range, TTL expired) running against a real PostgreSQL container via Testcontainers