Refactor mono wrap method

[Aleexender]

Description:
This refactoring improves the maintainability and readability of the Mono.wrap method through the following changes:

1. Extract Mono source creation logic into a separate method (createMonoSource)

   • Reduces cognitive complexity of the main wrap method
   • Makes the source creation logic more focused and easier to maintain

2. Simplify conditional logic using ternary operators

   • Reduces nesting levels in the code
   • Makes the flow control more straightforward

3. Improve type handling consistency

   • Refined type casting structure following existing patterns
   • Maintained consistent use of SuppressWarnings annotations in line with the codebase's existing conventions

The changes maintain the exact same functionality while making the code structure clearer and more maintainable.

[Aleexender]

@chemicL hello!
I'm curious about why the testLeakWithRetryWhenImmediatelyCancelled() test in the core-java21 CI pipeline is failing.
While it runs perfectly fine in my local environment, I'm wondering if my changes could have inadvertently caused this issue.