[DISCO-3583] Add client for Merino Suggest

[misaniwere]

• [DISCO-3583]
• This PR adds a new suggest module to the merino crate with a SuggestClient that calls the Merino /api/v1/suggest endpoint and is exposed to iOS and Android through UniFFI
• Also added a suggest subcommand to merino-cli for local testing.

Changes

• SuggestClient: the public UniFFI object exposed to iOS/Android. Takes a SuggestConfig (optional base host override) and exposes a get_suggestions(query, options) method that returns the raw JSON response body as a string.
• SuggestOptions: a UniFFI record mapping all merino suggest query parameters (providers, source, country, region, city, client_variants, request_type, accept_language). All fields are optional and omitted fields are not sent.
• uses viaduct's send_sync with an OHTTP channel ( "merino")

QA

• Can be QA'd be running tests: cargo test -p merino suggest
• Also locally hitting the endpoint using prod and ohttp: cargo run -p merino-cli -- suggest --query "apple"
• Confirm curated recommendations command still works:
  cargo run --bin merino-cli -- recommendations --user-agent "my-cli/1.0" --json '{ "locale": "en", "region": "US", "count": 4, "topics": ["tech"], "feeds": ["sections"] }'

Pull Request checklist

• Breaking changes: This PR follows our breaking change policy
  • This PR follows the breaking change policy:
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  • Any new dependencies are accompanied by a summary of the due diligence applied in selecting them.