Add additional Prebid debug flags to OpenRTB requests

[ChristianPavilonis]

Summary

Adds additional debug flags to Prebid/OpenRTB bid requests when debug: true is set in the prebid integration config, and surfaces Prebid Server debug response data in the /auction endpoint response.

Changes

OpenRTB request debug flags (openrtb.rs, prebid.rs)

When config.debug is enabled, the outgoing OpenRTB request now includes:

{
  "test": 1,
  "ext": {
    "prebid": {
      "debug": true,
      "returnallbidstatus": true
    }
  }
}

• test: 1 — standard OpenRTB 2.x test mode flag
• ext.prebid.debug: true — enables Prebid Server debug output (already existed)
• ext.prebid.returnallbidstatus: true — includes all bid statuses (rejected/no-bid reasons) in the response

All three fields are None and omitted from serialization when debug is disabled (default).

Response debug logging (prebid.rs)

Added log::debug! of the full Prebid Server response JSON in parse_response(), gated on both config.debug and log::log_enabled!(Level::Debug) to avoid wasted serialization.

Debug data in /auction response (prebid.rs)

Extracted enrich_response_metadata() method that attaches Prebid Server response metadata to AuctionResponse.metadata, which flows through ProviderSummary → provider_details in the /auction response ext:

Always-on fields (present whenever PBS returns them):

• responsetimemillis — per-bidder response times
• errors — per-bidder errors
• warnings — per-bidder warnings (new)

Debug-gated fields (only when config.debug is true):

• debug — full ext.debug blob (httpcalls, resolvedrequest)
• bidstatus — per-bid status array from ext.prebid.bidstatus

Safety

• Startup log::warn! emitted when debug: true is configured, alerting operators that debug data will be included in /auction responses
• All debug fields default to None/omitted — no behavior change when debug is disabled

Tests

• to_openrtb_includes_debug_flags_when_enabled — verifies struct values and serialized JSON shape
• to_openrtb_omits_debug_flags_when_disabled — verifies fields are None and omitted from JSON
• enrich_response_metadata_attaches_always_on_fields — verifies always-on metadata present, debug-gated fields absent
• enrich_response_metadata_includes_debug_fields_when_enabled — verifies debug + bidstatus present with correct values

Tested and working on my test site

[ChristianPavilonis]

Do we want this in the /auction response, or are debug logs good?
The no bids don't tell us a lot (no headers or anything comes back)

[aram356]

Let's return response if prebid integration is enabled with debug = true