feat: make qsOptions property protected to enable inheritance

BREAKING CHANGE: Changed `qsOptions` property from private to protected to allow
subclasses to access internal state. This enables better extensibility but
may affect consumers who subclass DrupalJsonApiParams.

- Changed `private qsOptions` to `protected qsOptions` in DrupalJsonApiParams class
- Allows subclasses to access and modify internal qsOptions state
- Improves library extensibility for advanced use cases

Author: d34dman

src/index.ts

@@ -69,7 +69,7 @@ export class DrupalJsonApiParams implements DrupalJsonApiParamsInterface {
     fields: {},
   };
 
-  private qsOptions: object = {};
+  protected qsOptions: object = {};
 
   private config: DrupalJsonApiParamConfig = {
     useShortCutForQueryGeneration: true,