fix: use /pulses/activity endpoint instead of /pulses/subscribed

[root-Brainoverflow]

Description

This PR fixes the OTX-Python-SDK by switching from the /pulses/subscribed endpoint to /pulses/activity endpoint, which resolves persistent 504 Gateway Timeout errors.

Changes:

• Update SUBSCRIBED constant to use /pulses/activity endpoint
• Add comment explaining the change

Root Cause:
The /pulses/subscribed endpoint consistently returns 504 Gateway Timeout after 30+ seconds, making the SDK unusable.

Testing:

• Successfully tested with valid API key
• Confirmed /pulses/activity returns identical data structure
• All pulse fetching methods now work without timeouts

API Comparison:

Endpoint	Status	Response Time
/api/v1/pulses/subscribed	TIMEOUT	30s+
/api/v1/pulses/activity	SUCCESS	less than 2s

Fixes #ISSUE_NUMBER

Type of change

• Bug fix (non-breaking change which fixes an issue)

Backward Compatibility

This change is backward compatible. Both endpoints return the same data structure, so existing code will continue to work without modification.

Testing

Tested with:

• Python 3.12
• OTX-Python-SDK 1.5.12
• Valid AlienVault OTX API key

Example working code after fix:

from OTXv2 import OTXv2
from datetime import datetime

otx = OTXv2("YOUR_API_KEY")
pulses = otx.getsince(datetime(2026, 3, 1))  # Now works successfully

Checklist

• My code follows the style guidelines of this project
• I have tested my code and it works as expected
• This change maintains backward compatibility
• No breaking changes introduced

Related issue: #82