Add route_request dispatch coverage

[ChristianPavilonis]

Summary

• Add focused Fastly adapter route_request dispatch coverage.
• Cover static TSJS success and unknown bundle handling.
• Cover public discovery and unauthenticated admin dispatch.
• Cover auction dispatch through consent-dependent setup.
• Cover unknown-route publisher fallback dispatch without configured consent persistence.

Closes #451

Tests

• cargo test -p trusted-server-adapter-fastly route_tests -- --nocapture
• cargo fmt --all -- --check
• cargo test --workspace
• cargo clippy --workspace --all-targets --all-features -- -D warnings

[prk-Jr]

Summary

This PR adds focused Fastly adapter coverage for route_request. The overall direction is useful, but one assertion currently does not prove the route branch it is intended to cover because another branch can produce the same failure status.

CI Status

• cargo fmt: PASS
• cargo test: PASS
• vitest: PASS
• integration tests: PASS
• browser integration tests: PASS
• CodeQL: PASS
• analysis jobs: PASS