feat: Add NetEvolve.Pulse.Redis with RedisIdempotencyStore

[Copilot]

Adds a Redis-backed idempotency provider using StackExchange.Redis atomic SET NX EX operations, eliminating the read-before-write round-trip inherent in SQL-based stores.

New project: NetEvolve.Pulse.Redis

• RedisIdempotencyKeyOptions — KeyPrefix ("pulse:idempotency:"), TimeToLive (24h), Database (-1)
• RedisIdempotencyKeyOptionsValidator — rejects TimeToLive <= Zero and empty/whitespace KeyPrefix; registered with ValidateOnStart()
• RedisIdempotencyKeyOptionsConfiguration — binds from Pulse:Idempotency:Redis config section; gracefully no-ops when IConfiguration is not registered
• RedisIdempotencyStore : IIdempotencyStore — directly implements IIdempotencyStore (bypasses the IIdempotencyKeyRepository layer); ExistsAsync → KeyExistsAsync; StoreAsync → StringSetAsync(..., When.NotExists), silently succeeds on duplicate
• AddRedisIdempotencyStore — replaces the default IIdempotencyStore registration with RedisIdempotencyStore (Scoped); IConnectionMultiplexer must be registered by the caller

// Register IConnectionMultiplexer first
services.AddSingleton<IConnectionMultiplexer>(_ =>
    ConnectionMultiplexer.Connect("localhost:6379"));

services.AddPulse(config => config
    .AddRedisIdempotencyStore(opts =>
    {
        opts.KeyPrefix = "myapp:idempotency:";
        opts.TimeToLive = TimeSpan.FromHours(48);
    })
);

Test coverage

Unit tests cover constructor validation, argument guards, ExistsAsync true/false propagation, and StoreAsync no-throw on duplicate. Added <NoWarn>SER002;SER003;SER006</NoWarn> to the unit test project to suppress StackExchange.Redis experimental-API diagnostics emitted by the TUnit.Mocks source generator.