fix(postgrest): wrap error in PostgrestError instance on processResponse

[Vansh1811]

Problem

The error field returned by processResponse in PostgrestBuilder is a plain object literal, not an instance of PostgrestError. This means error instanceof PostgrestError checks always return false, breaking error type-narrowing for consumers.

Related issue: supabase/postgrest-js#1643

Fix

Wrap the error field in the final return statement with new PostgrestError(error) when the error is non-null, so that instanceof checks work correctly.

// Before
error,

// After
error: error ? new PostgrestError(error) : null,

This is consistent with the existing throw new PostgrestError(error) on line 460 for the shouldThrowOnError path.

Testing

Consumers can now reliably narrow the error type:

const { error } = await supabase.from('table').select()
if (error instanceof PostgrestError) {
  // This now works correctly
  console.log(error.code, error.message)
}

[steve-chavez]

Related issue: supabase/postgrest-js#1643

I'm unable to find the reference so don't understand the motivation here, please share the full link.