Node: Reduce Non-Null Assertions about BaseClient's config

[jhpung]

Description

I noticed that while the BaseClient constructor's options parameter is marked as optional (options?: BaseClientConfiguration), it's always provided with a non-null value in all creation paths through createClient()[1][2]. This creates an unnecessary nullable context that leads to multiple non-null assertions (!)[1][2][3] throughout the codebase.

This change would make the code more straightforward and remove potentially confusing null-checking context for developers first encountering the codebase. The nullable parameter currently serves no practical purpose since options are always provided during client creation.

Checklist

• Make the options parameter required or give default value (e.g. {}) in the BaseClient constructor
• Remove non-null assertions where this.config is used
• Simplify the type safety guarantees

Additional Notes

No response