all-time contributed-to, contribs to own repos refinements

[marcalexiei]

• Refinements for all-time contributed-to, contribs to own repos #528

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• New common/date.ts, exposes
  • getGitHubYearRange
  • toGitHubDateTime
  • dateDiff (moved from ops.ts);
    the three places that built a year's UTC bounds now share it.
• ?commits_year must be a four-digit year,
  rejected at the api boundary as error - permanent instead of NaN or a temporary error later.
• All-time contributed-to fetcher: filters own repos by user.login,
  selects repositoryContributions only when own repos are requested (saves nodes),
  and caps each request at MAX_RANGES_PER_REQUEST aliases.
• Simplified that fetcher into one function with a shared graphqlError helper;
  own repos are skipped while collecting and the no-op roundToNearestMidnight is gone.
• fetchStats.test.ts: fixtures are typed against the generated query types,
  and fetchStatsWith / expectedStats helpers replace the positional calls and repeated expectation blocks.

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