Migrate HealthChecks.Network tests to Testcontainers

[monofunc]

What this PR does / why we need it:

• Add Testcontainers fixtures to HealthChecks.Network tests

Which issue(s) this PR fixes: Contributes to #2335

Please reference the issue this PR will close: #1018

Special notes for your reviewer: I explicitly set the TLS mode in some SMTP tests named _auto_* because Testcontainers maps random ports, while AUTO mode expects specific ports like 465 or 587. We can cover the AUTO mods with unit tests later.

Does this PR introduce a user-facing change?: No

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

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.81%. Comparing base (72d9abf) to head (8bd2a31).
⚠️ Report is 40 commits behind head on master.
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2422      +/-   ##
==========================================
+ Coverage   66.88%   73.81%   +6.93%     
==========================================
  Files         268       35     -233     
  Lines        8730      928    -7802     
  Branches      631      119     -512     
==========================================
- Hits         5839      685    -5154     
+ Misses       2723      212    -2511     
+ Partials      168       31     -137     

Flag	Coverage Δ
ApplicationStatus	?
ArangoDb	?
Aws.S3	?
Aws.SecretsManager	?
Aws.Sns	?
Aws.Sqs	?
Aws.SystemsManager	?
Azure.IoTHub	?
AzureApplicationInsights	?
AzureBlobStorage	?
AzureDigitalTwin	?
AzureEventHubs	?
AzureFileStorage	?
AzureKeyVault	?
AzureQueueStorage	?
AzureSearch	?
AzureServiceBus	?
AzureTableStorage	?
Consul	?
CosmosDb	?
Dapr	?
DocumentDb	?
DynamoDb	?
Elasticsearch	?
EventStore	?
EventStore.gRPC	?
Gcp.CloudFirestore	?
Gremlin	?
Hangfire	?
IbmMQ	?
InfluxDB	?
Kafka	?
Kubernetes	?
Milvus	?
MongoDb	?
MySql	?
Nats	?
Network	73.81% <ø> (?)
Npgsql	?
OpenIdConnectServer	?
Oracle	?
Prometheus.Metrics	?
Publisher.ApplicationInsights	?
Publisher.CloudWatch	?
Publisher.Datadog	?
Publisher.Prometheus	?
Publisher.Seq	?
Qdrant	?
RabbitMQ	?
RavenDb	?
Redis	?
SendGrid	?
SignalR	?
SqlServer	?
Sqlite	?
System	?
UI	?
Uris	?

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