fix(dataforseo): honor SERP market and language code overrides

[rudycelekli]

Problem and change

The advertised SERP code flags were ignored, so an explicitly selected market could still request United States/English. Codes now take precedence over names, and invalid location codes or missing language-code values are rejected before requesting a paid report.

Validation

• 5 focused regression/control tests pass; 4 cases failed against unchanged upstream before the fix.
• Native child CLI runs with intercepted fetch; no authenticated provider requests were made.
• Tested on Node 18.20.8 and Node 24.19.0; syntax, usage/dry-run, diff and repository version gates checked.
• Run: node --test tests/dataforseo-market.test.cjs

Contract reference

• https://docs.dataforseo.com/v3/serp/google/organic/live/regular/

Assistance

AI-assisted implementation and test development; patch and contract fixtures reviewed before publication.