feat(quota): add usage tracking for Groq
First slice of #3701: quota tracking for Groq via x-ratelimit-* response
headers on the models endpoint (no dedicated quota endpoint exists, and
reading usage costs zero tokens).
- usage/groq.js: parse request+token limit/remaining headers; Go-style
duration reset headers ("2m59.56s") resolve to future timestamps;
missing key/401/403 -> message, 2xx without headers -> soft
"not tracked yet" with quotas:{}
- registry/groq.js: transport.usage.url (reuses validateUrl) +
features {usage, usageApikey}
- services/usage.js: groq entry in USAGE_HANDLERS
- ProviderLimits/utils.js: parseQuotaData case (absolute used/total,
codex/kiro style)
- tests: groq-usage.test.js (registry flags, header parsing, soft
not-tracked path, missing key/401, parseQuotaData)
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