feat: add env helper for polymarket examples

[JonesRoy3]

Added the examples/print-env.ts script, which helps you quickly check that environment variables for SDK examples are set correctly.

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Note

Add examples/print-env.ts to quickly verify required Polymarket example environment variables.

• Examples:
  • New script: examples/print-env.ts to validate presence of env vars used by examples.
    • Checks POLYMARKET_API_BASE, POLYMARKET_API_KEY, POLYMARKET_WALLET_PRIVATE_KEY, POLYMARKET_NETWORK and masks values in output.

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