feat: module level singleton pattern For Pulse instantiation

[aanshu-ss]

Background: If Pulse object is initialized twice it gives us a warning like this:
Overriding of current LoggerProvider is not allowed"

We want the Pulse SDK to be initialized only once per kernel, so that any notebook connected to a kernel has access to a singleton pulse object. This works as expected when a new kernel is started.
However, issues arise when the feature flag (FF) is changed and the notebook page is reloaded. In some cases, the reload starts a new kernel (which is fine), but other times it reconnects to an existing idle kernel. If that kernel was initialized before the FF change, it may not have the correct pulse object, leading to inconsistent behavior.
Since we rely on having a single, correctly-initialized pulse instance per kernel, we need to address this.

Hence, we use module level singleton pattern for Pulse class. where the global state is maintained at the module level.

Testing

Tested locally and test case updated.Pulse is instantiated before also, and when we re-instantiate it again, it skips the reinstantiation with message: Pulse instance already exists. Skipping initialization.

JIRA

https://memsql.atlassian.net/browse/MCDB-74788