fix: incorrect Ecosystem enum interpolation in SerpApi query

[vbelouso]

Fixes a bug where the Ecosystem enum member was being stringified directly into the SerpApi search query (e.g. Ecosystem.GO), instead of using its value (go).

This resulted in malformed search queries that could reduce search result quality.

Before: Query contained part+of+the+Ecosystem.GO+standard+library, which is not natural language.
After: Query contains part+of+the+go+standard+library.

Example of issue (from logs):

[09/Jan/2026:13:39:52 +0000] traceId: - - (MISS) "GET /serpapi/search?engine=google&google_domain=google.com&gl=us&hl=en&api_key=FAKE&q=Is+'github.com/golang/crypto/jwt'+part+of+the+Ecosystem.GO+standard+library?&source=python&serp_api_key=FAKE&output=json HTTP/1.1" 401 - 108 bytes {10.130.3.188} "Python/3.12 aiohttp/3.12.15" 0.032 - 1. Auth: [NOT PROVIDED]
2026/01/09 13:39:52 [info] 77#77: *53 client 10.130.3.188 closed keepalive connection

[zvigrinberg]

@vbelouso Good catch!
Approved.