Add TCF 2.3 Disclosed Vendors segment support (#40)

[ggierak]

Summary

• Add support for parsing the Disclosed Vendors segment (SegmentType=1) introduced in TCF 2.3
• Expose two new methods on the VendorConsents interface: MaxDisclosedVendorID() and DisclosedVendor(id)
• Maintain full backward compatibility with TCF 2.2 strings (methods return 0 / false when the segment is absent)

Details

TCF 2.3 makes the Disclosed Vendors segment mandatory in TC Strings:

[Core String].[Disclosed Vendors].[Publisher TC]

This segment records which vendors were disclosed to the user by the CMP. Previously, ParseString() discarded all segments after the first . separator. Now it decodes each additional segment, identifies its type via the first 3 bits, and parses Disclosed Vendors (type 1) using the same bitfield/range encoding as vendor consent.

Changes

File	Change
api/consent.go	Add MaxDisclosedVendorID() and DisclosedVendor(id) to VendorConsents interface
vendorconsent/tcf2/consent.go	Parse additional segments in ParseString(), add parseDisclosedVendors() and parseSegmentRangeSection()
vendorconsent/tcf2/metadata.go	Add disclosedVendors field and accessor methods with nil-safe handling
vendorconsent/tcf1/metadata.go	Stub implementations returning zero-values
vendorconsent/tcf2/consent_test.go	Tests for TCF 2.3 parsing, TCF 2.2 backward compat, and edge cases

Test plan

• Parse TCF 2.3 string with range-encoded Disclosed Vendors (vendors 1-5, 100, 404)
• Parse TCF 2.2 string without Disclosed Vendors segment (returns 0/false)
• Edge cases: vendor ID 0 and beyond MaxDisclosedVendorID
• Existing tests pass (go test ./...)

[osazos]

Hi @ggierak, thanks for working on this. There is already an open PR addressing the same issue (#48), and it’s currently under review and close to being ready (see onfocusio#1).
Would you mind joining the discussion there and contributing to that PR so we can avoid duplicating efforts?