Improved Subfinder SDK Usability

The current subfinder Go module has limited functionality as an SDK. While it allows configuring the runner and performing enumerations, obtaining results requires passing through writers and parsing the output again, which is inefficient for programmatic use.

This pull request introduces a change to make the subfinder module more SDK-friendly by directly returning the sourceMap. The sourceMap contains the enumerated subdomains along with the sources that identified them, eliminating the need to reprocess the output.

Key Changes

• Modified the enumeration logic to return the sourceMap as a result.
• Kept changes minimal to minimize the impact on other parts of the codebase.
• Modified example code to use subfinder Go module to use the sourceMap.