Add custom fetch and httpAgent support

[demoncoder-crypto]

Feature Request: Custom Fetch and HTTP Agent Support

Description

Adds support for custom fetch implementations and Node.js httpAgent configuration per #288.

Key Changes

1. Added fetch and httpAgent to RequestOptions interface

Security Notes

• httpAgent enables proper SSRF protection through proxy configuration
• Custom fetch allows request validation/redirection
• Important: All tests using real API keys should be run in protected environments

Implementation

The implementation adds two new properties to the RequestOptions interface:

export interface RequestOptions 
{

  fetch?: typeof fetch;

  httpAgent?: any;
}

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