send permutive segments to adserver

[ChristianPavilonis]

Passes Permutive audience segments from the browser through to the ad server mediation endpoint, enabling segment-targeted ad decisioning.

• Introduces a context provider registry on the JS side (context.ts) — a generic mechanism for integrations to contribute data to auction requests without core needing integration-specific knowledge.
• The Permutive integration registers a context provider that reads cohort segments from localStorage (permutive-app key) and injects them as permutive_segments in the request config.
• On the Rust side, convert_tsjs_to_auction_request now forwards all config entries into the AuctionRequest.context map instead of discarding them.
• The AdServer Mock provider reads permutive_segments from the context and appends them as a ?permutive=seg1,seg2,... query parameter on the mediation endpoint URL.
  Changes

Layer	File	What
JS core	core/context.ts (new)	Context provider registry (registerContextProvider, collectContext)
JS core	core/request.ts	Calls collectContext() to build config payload
JS integration	integrations/permutive/segments.ts (new)	Reads segments from localStorage (core.cohorts.all primary, eventUpload fallback)
JS integration	integrations/permutive/index.ts	Registers context provider with Permutive segments
Rust common	auction/formats.rs	Forwards config entries into AuctionRequest.context
Rust common	integrations/adserver_mock.rs	build_endpoint_url() appends ?permutive= query param
Tests	context.test.ts, segments.test.ts, Rust unit tests	Full coverage for new functionality

Closes #132

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How to Manually Test

1. Verify Permutive segment extraction (JS)
2. Open a publisher page that has Permutive active (or any page where you can set localStorage manually).
3. Open DevTools Console and confirm localStorage.getItem('permutive-app') has data — look for core.cohorts.all containing segment IDs.
4. If testing without a real Permutive install, seed it manually:

      localStorage.setItem('permutive-app', JSON.stringify({
     core: { cohorts: { all: ['10000001', '10000003', 'adv', 'bhgp'] } }
   }));

5. Load the page with the tsjs tag. In the DevTools Console, filter for context — you should see a log like:
   requestAds: payload { units: N, contextKeys: ["permutive_segments"] }

6. Verify segments are sent to the server

7. Open DevTools Network tab and filter for /auction.

8. Trigger an ad request.

9. Inspect the /auction POST request body — the config object should contain:

      {
     config: {
       permutive_segments: [10000001, 10000003, adv, bhgp]
     }
   }