fix: add builder auth support to get_order and get_orders

[suhailkakar]

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Note

Low Risk
Small, localized change that only affects request headers for two GET endpoints and falls back to existing behavior if builder header generation fails.

Overview
Adds optional builder authentication handling to ClobClient.get_orders and ClobClient.get_order by attempting to generate builder headers and using them when available.

This brings these read endpoints in line with existing builder-header usage on order-posting calls, while preserving the existing Level 2 header flow as a fallback.

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