fix(core): allow null for BrowserView.ptr type null assignment

[AhmedNAgy25]

What

Fixes a TypeScript type safety issue in BrowserView by properly allowing null values for the ptr property.

• Changed ptr from Pointer! (non-null assertion) to Pointer | null = null
• Removed null as any type hack in the remove() method

Why

The ptr property represents a native pointer that becomes invalid after remove() is called. The previous code set it to null but the type didn't reflect this, requiring a type cast hack (as any) to work around TypeScript.

This fix:

• Makes the types accurately represent the runtime behavior
• Removes the type hack for cleaner code
• Prevents potential runtime errors from improper null handling

[YoavCodes]

Thanks!