Make AddHealthieRedis one method, because two could not be told apart

[ivanvyd]

AddHealthieRedis("localhost:6379") did not register a Redis connection. It registered "localhost:6379" as a key prefix.

There were two overloads:

AddHealthieRedis(this IServiceCollection, string configuration, string keyPrefix = Default)
AddHealthieRedis(this IServiceCollection, string keyPrefix = Default)

Given a single string argument, C# prefers the second — no optional parameter left unfilled. So the connection string silently became the prefix, no IConnectionMultiplexer was ever registered, and the failure surfaced later as:

System.InvalidOperationException: No service for type
'StackExchange.Redis.IConnectionMultiplexer' has been registered.

That is the exact call the package README documents, so the documented usage was broken.

Why nothing caught it

Every Redis test constructed RedisStateProvider directly. The provider had 15 tests and a 12-writer race; its registration had none. Well-covered code behind an unreachable front door.

The fix

One method, configuration optional. Pass it to have the connection opened; leave it out to use the one the application already registers. There is nothing left for overload resolution to get wrong, and keyPrefix has to be named to be passed alone.

Three new tests go through AddHealthieRedis rather than around it — with a configuration string, with an existing connection, and with only a named prefix. The first fails against the two-overload version:

the shipped two-overload form -> Failed! - Failed: 1

How it was found

By packing all 20 packages into a local feed and consuming them from a console project outside the repository — dotnet add package Healthie.NET.Redis, then actually running it against a real Redis. That is the only thing that exercises what a consumer is handed, and it is a step I had not taken for any package until now.

Verification

466 tests green on net8.0 and net10.0, 0 errors and 0 warnings on a cleaned build.