Add missing tests for load-balancer specification

[devin-ai-integration]

Add missing tests for load-balancer specification

This PR adds test files for several areas where test coverage is missing or incomplete for the load-balancer specification:

1. URI Validation: Tests for validating that an exception is thrown when loadBalanced=true is used with:

   • Multiple hosts in the connection string
   • replicaSet option
   • directConnection=true option
   • srvMaxHosts option with a positive integer value

2. DNS Seedlist Discovery: Tests for verifying that:

   • When a MongoClient is configured with an SRV URI and loadBalanced=true, the driver does not poll for changes in the SRV record

3. Server Discovery and Monitoring: Tests for verifying that:

   • The topology starts in type LoadBalanced and remains as LoadBalanced
   • The topology contains 1 ServerDescription with a ServerType of LoadBalancer
   • Required SDAM events are emitted in the correct order

4. Driver Sessions: Tests for verifying that:

   • Sessions are always supported in load balancer mode
   • ServerType of LoadBalancer is considered a data-bearing server

5. Log Messages: Tests for verifying that the relevant SDAM log messages are emitted

Link to Devin run: https://app.devin.ai/sessions/8a268de542e646cca085393b19ca74fe
Requested by: james.kovacs@mongodb.com

[devin-ai-integration]

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