Add CloakedCnameDetector and TrackerDataDownloader to the api

[aibrahim-]

Task/Issue URL: https://app.asana.com/1/137249556945/task/1216988666467280
Tech Design URL (if applicable): https://app.asana.com/1/137249556945/task/1216706645739239
API Proposals URL(s) (if applicable): to follow — will be added before merge

Description

Phase 2 of the tracker-detection extraction. No behaviour change.

• CloakedCnameDetector's interface moves out of :app into tracker-detection-api, keeping its package so WebViewRequestInterceptor needs no import change. CloakedCnameRefresher deliberately stays next to the implementation: its only consumer is TrackerDataLoader, so it travels with the impl rather than becoming public surface.
• TrackerDataDownloader becomes an interface in the api, mirroring the existing HttpsUpgradeDataDownloader (same Completable shape, and httpsupgrade-api is the precedent for rxjava in an api module). The interface keeps the legacy FQN so AppConfigurationDownloader, BlockList and TrackerDataDevReceiver are untouched; the concrete class becomes RealTrackerDataDownloader, bound with @ContributesBinding.

Steps to test this PR

TDS still downloads and CNAME cloaking is still detected

• Build and run an internal build
• Dev settings → trigger a tracker data (TDS) download and confirm it completes without error
• Visit a site known to use CNAME-cloaked trackers and confirm they are still blocked in the privacy dashboard

UI changes

Before	After
No UI changes	No UI changes

[github-actions]

⚠️ API Proposal reminder

This PR changes the public surface of one or more -api modules, but the API Proposals field of the PR description is empty. This is a non-blocking reminder — please double-check whether a proposal is needed.

Changed -api source files:

• tracker-detection/tracker-detection-api/src/main/java/com/duckduckgo/app/trackerdetection/CloakedCnameDetector.kt
• tracker-detection/tracker-detection-api/src/main/java/com/duckduckgo/app/trackerdetection/api/TrackerDataDownloader.kt

To clear this reminder, edit the PR description and either:

• add the approved API Proposal link(s) in the API Proposals field (one per line), or
• write None there if this PR does not change the public API (e.g. KDoc, comments, tests).

See the API Proposals section in .claude/docs/contributions.md for details.

[claude]

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