Honor applicable_intents in the Rust demo evaluator

[aleksUIX]

Summary

The Rust demo evaluator returned every mutation its auction arm defines, ignoring the request's applicable_intents. The Go implementation gates every mutation through IsIntentApplicable (internal/handlers/handlers.go), and RTBRequest.applicable_intents is documented as the list of intents the server is eligible to send back. A container proposing intents it was not offered violates that contract.

Example: samples/bid-shading.json declares only BID_SHADE applicable, but the Rust server responded with ACTIVATE_SEGMENTS and ACTIVATE_DEALS mutations as well.

Change

• bidder/evaluator.rs: mutations are now filtered against applicable_intents before the response is returned, with the same semantics as the Go implementation (empty list means all intents are applicable).
• Tests: three new evaluator tests cover the restricted, empty, and no-match cases; the bid-shading sample expectation drops from 3 mutations to 1.

Verification

• cargo test: 16 passed
• Live gRPC call with samples/bid-shading.json now returns only the BID_SHADE mutation:

{
  "id": "sample-bidshade-001",
  "mutations": [
    {
      "intent": "BID_SHADE",
      "op": "OPERATION_REPLACE",
      "path": "/seatbid/dsp-001/bid/bid-abc",
      "adjustBid": { "price": 4.675 }
    }
  ],
  ...
}

Note

Stacked on #13 (builds on its evaluator routing fix and test suite). The first commit in the diff belongs to that PR and will drop out once it merges; independent of #14.