test: refactor reload test

[burningalchemist]

This pull request refactors the test configuration generation in reload_test.go to use strongly-typed Go structs and YAML marshaling instead of manual string formatting. This makes the configuration generation more robust and maintainable. It also adds minor improvements to test logging and disables logging output during tests.

Test configuration improvements:

• Rewrote the writeConfig helper to build the YAML config using Go struct types and yaml.Marshal, replacing the previous string concatenation approach. This reduces errors and improves maintainability.
• Updated call sites to the new writeConfig signature, which now infers the number of targets from the provided directories.

Test reliability and output:

• Added a TestMain function to set the default logger to discard output, preventing unwanted log messages during test runs. [1] [2]
• Improved the error message in the goroutine leak check for clarity.

Minor code hygiene:

• Fixed a bug in setupCSVDirs where the loop incorrectly ranged over an integer instead of the directory slice.