Clean up dead GDPR country code in geo.rs and reconcile Eid/Uid types

[ChristianPavilonis]

Context

After rebasing the consent management branch onto main (which introduced the trusted_server_openrtb shared crate), there are a few cleanup items that don't belong in the consent PR itself.

Items

1. Dead is_gdpr_country in geo.rs (medium priority)

crates/common/src/geo.rs defines is_gdpr_country() and a static GDPR_COUNTRIES HashSet (lines 114-136). This function is now only called by its own tests — production code uses the config-driven consent_config.gdpr.applies_in list via consent::jurisdiction::detect_jurisdiction() instead.

There are now two independent GDPR country lists maintained in:

• crates/common/src/geo.rs:114 — LazyLock<HashSet<&str>>
• crates/common/src/consent_config.rs:20 — const GDPR_COUNTRIES: &[&str]

They're identical today but could drift. The geo.rs version should be removed and its tests deleted (or migrated to test the consent config default).

2. Local Eid/Uid vs shared crate types (low priority, future work)

crates/common/src/openrtb.rs defines local Eid and Uid structs (lines 73-93) that are structurally different from the shared trusted_server_openrtb::Eid/Uid:

Field	Local	Shared
Eid.source	String (required)	Option<String>
Eid.inserter/matcher/mm/ext	Missing	Present
Uid.id	String (required)	Option<String>
Uid.atype	Option<u8>	Option<i32>
Uid.ext	Option<Value>	Option<Map<String,Value>>

The local types are used by UserExt.eids, which is currently always None (pre-positioned for future EID support). When EID identity provider integration is implemented, the PR should decide whether to:

• Use the shared crate's Eid/Uid types directly (richer, spec-complete)
• Keep the local simplified types with a conversion layer
• Remove the local types entirely

No action needed until EID support goes live.

Acceptance Criteria

• Remove is_gdpr_country(), GDPR_COUNTRIES HashSet, and associated tests from geo.rs
• Verify no other production code depends on is_gdpr_country
• All CI gates pass after removal