Add Rest() and RestError() methods - Fixes #29

[AdvaitP-1]

What kind of change does this PR introduce?

Feature - Adds methods to access the underlying PostgREST client and its error state

What is the current behavior?

The rest field in the Client struct is private, so users can't:

• Call PostgREST methods like ChangeSchema() directly
• Access the ClientError from the PostgREST client
• Write custom wrappers that need direct client access

This addresses issue #29

What is the new behavior?

Added two new methods:

• Rest() - Returns the underlying PostgREST client for direct access:
  restClient := client.Rest()
  restClient.ChangeSchema("custom_schema")

• RestError() - Returns the last error from the PostgREST client:
  if err := client.RestError(); err != nil {
  log.Printf("PostgREST error: %v", err)
  }