fix: correct getCollectionOffers return type and add pagination support

[ryanio]

Summary

This PR fixes a type mismatch in the getCollectionOffers method, corrects invalid AssetEventType enum values, and bumps the package version:

• Fixed getCollectionOffers return type from ListCollectionOffersResponse | null to GetOffersResponse
• Added pagination parameters (limit, next) to getCollectionOffers method
• Removed invalid AssetEventType enum values (CANCEL, REDEMPTION)
• Updated documentation to reflect only valid event types
• Bumped package version from 8.0.5 to 8.0.6

Background

During an audit of OpenSea API v2 endpoints against the opensea-js implementation, I discovered:

1. getCollectionOffers type mismatch: Testing with the actual API endpoint confirmed it returns { "offers": [...], "next": "..." } which matches GetOffersResponse (with pagination cursor), not ListCollectionOffersResponse (which lacks pagination).

2. Invalid AssetEventType values: API testing revealed that CANCEL and REDEMPTION are not valid event types. The API only accepts:

   • ✅ order - New listings and offers
   • ✅ sale - NFT sales
   • ✅ transfer - NFT transfers (including mints from 0x0 address)
   • ❌ cancel - Returns API error
   • ❌ redemption - Returns API error

Changes

API Implementation

• src/api/offers.ts: Changed return type to GetOffersResponse and added limit/next parameters
• src/api/api.ts: Updated wrapper method signature and removed unused ListCollectionOffersResponse import
• src/api/types.ts: Removed CANCEL and REDEMPTION from AssetEventType enum

Tests

• test/api/offers.spec.ts: Updated all 5 unit tests to use GetOffersResponse and added pagination tests
• test/integration/getCollectionOffers.spec.ts: Added proper null check for offer.criteria

Documentation

• developerDocs/api-reference.md: Updated event types list, removed invalid types
• developerDocs/getting-started.md: Updated event types list, removed invalid types

Version

• package.json: Bumped version from 8.0.5 to 8.0.6

Testing

• ✅ All unit tests pass (npm test)
• ✅ Type checking passes (npm run check-types)
• ✅ Linting passes (npm run lint)
• ✅ Prettier formatting passes (npm run prettier:check)
• ✅ Build passes (npm run build)
• ✅ Verified with real API calls using live OpenSea API

API Verification

Tested all event types with live API:

# Valid - returns events
curl -H "X-API-KEY: ***" "https://api.opensea.io/api/v2/events?event_type=order&limit=1"
curl -H "X-API-KEY: ***" "https://api.opensea.io/api/v2/events?event_type=sale&limit=1"
curl -H "X-API-KEY: ***" "https://api.opensea.io/api/v2/events?event_type=transfer&limit=1"

# Invalid - returns error
curl -H "X-API-KEY: ***" "https://api.opensea.io/api/v2/events?event_type=cancel&limit=1"
# {"errors":["Invalid value for parameter 'event_type'. Invalid event_type: cancel"]}

curl -H "X-API-KEY: ***" "https://api.opensea.io/api/v2/events?event_type=redemption&limit=1"
# {"errors":["Invalid value for parameter 'event_type'. Invalid event_type: redemption"]}

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