Remove private static cache from RabbitMQHealthCheck

[eerhardt]

What this PR does / why we need it:

RabbitMQHealthCheck is maintaining it's private static cache of instances. It's wrong, as it can cause a memory leak (it won't ever be freed).

Moreover, it's can create instances of IConnection. This is wrong, as it can lead into a situation when we have multiple instances of IConnection that are connected to the same server: one used by the app and another created and used by the health check. And we should have only one.

We should do the same as in #2040, #2116 and #2096

I left RabbitMQ.v6 as-is to limit the breaking change. Only when an existing user moves from RabbitMQ.Client v6 to v7 will they need to update their health check (along with other breaking changes in RabbitMQ.Client).

Does this PR introduce a user-facing change?:

Yes, this is a breaking change to the RabbitMQ health check.

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Unit tests passing
• End-to-end tests passing
• Extended the documentation
• Provided sample for the feature

Copilot reviewed 6 out of 14 changed files in this pull request and generated 1 suggestion.

Files not reviewed (8)

• src/HealthChecks.Rabbitmq.v6/HealthChecks.Rabbitmq.v6.csproj: Language not supported
• src/HealthChecks.Rabbitmq/HealthChecks.Rabbitmq.csproj: Language not supported
• test/HealthChecks.RabbitMQ.Tests/HealthChecks.Rabbitmq.approved.txt: Language not supported
• test/HealthChecks.RabbitMQ.v6.Tests/HealthChecks.RabbitMQ.v6.Tests.csproj: Language not supported
• test/HealthChecks.RabbitMQ.Tests/Functional/RabbitHealthCheckTests.cs: Evaluated as low risk
• test/HealthChecks.RabbitMQ.v6.Tests/DependencyInjection/RegistrationTests.cs: Evaluated as low risk
• test/HealthChecks.RabbitMQ.v6.Tests/Functional/RabbitHealthCheckTests.cs: Evaluated as low risk
• src/HealthChecks.Rabbitmq/RabbitMQHealthCheck.cs: Evaluated as low risk

Comments skipped due to low confidence (1)

test/HealthChecks.RabbitMQ.Tests/DependencyInjection/RegistrationTests.cs:16

• The test should verify that the health check fails gracefully if no IConnection or IConnectionFactory is registered. Add a test case to ensure proper error handling in this scenario.

.AddRabbitMQ();

[adamsitnik]

LGTM, thanks a lot for your help @eerhardt !

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 94.44444% with 5 lines in your changes missing coverage. Please review.

Project coverage is 66.47%. Comparing base (72d9abf) to head (900b39c).
Report is 17 commits behind head on master.

Files with missing lines	Patch %	Lines
...yInjection/RabbitMQHealthCheckBuilderExtensions.cs	92.85%	2 Missing and 3 partials ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2343      +/-   ##
==========================================
- Coverage   66.88%   66.47%   -0.41%     
==========================================
  Files         268      254      -14     
  Lines        8730     8514     -216     
  Branches      631      606      -25     
==========================================
- Hits         5839     5660     -179     
+ Misses       2723     2693      -30     
+ Partials      168      161       -7     

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RabbitMQ	58.21% <94.44%> (+7.57%)	⬆️

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