Fix javadoc crawler reading a Maven Central index that stopped updating

[thswlsqls]

Fixes #8792

Description

• JavaDocsCrawler queries search.maven.org/solrsearch, whose index stopped updating on 2025-06-06 and reports latestVersion=1.51.0 for every io.opentelemetry artifact.
• Switch to central.sonatype.com/solrsearch. It is absent from Sonatype's REST API guide, but their FAQ says that index refreshes within minutes of a release while search.maven.org's does not (https://central.sonatype.org/faq/what-happened-to-search-maven-org/), and Apache's maven-indexer ships the same host as SmoSearchBackendFactory.CSC_SMO_URI.
• The hosts read start differently, so getArtifacts sends one request with rows=500 and no start, failing if it receives fewer documents than numFound.
• Runs 34300382073 and 34177613796 each log 246 Skipping crawling lines and no Crawling line, yet exit success. The fix restores 168 crawl requests across five groups.
• Triggering javadoc.io's lazy loading is the module's intent, not measured here.
• Follow-up idea: fail the job when nothing is crawled.

Testing done

• Replaced testGetArtifactsHandlesPagination with testGetArtifactsUsesASingleRequest (one request; URI has rows=500, no start=) and testGetArtifactsFailsOnIncompleteResponse (short response throws IOException naming the group).
• ./gradlew :javadoc-crawler:check passes; both new tests fail against the unpatched code.
• Unpublished module: no apidiff or API change.

[opentelemetry-pr-dashboard]

Pull request dashboard status

Waiting on maintainers · refreshed 2026-09-12 12:19 UTC

Merge when ready.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.26%. Comparing base (fb5023e) to head (e8cce37).
⚠️ Report is 14 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8796      +/-   ##
============================================
+ Coverage     91.25%   91.26%   +0.01%     
- Complexity    10512    10525      +13     
============================================
  Files          1007     1008       +1     
  Lines         28386    28465      +79     
  Branches       3591     3617      +26     
============================================
+ Hits          25904    25980      +76     
+ Misses         1687     1685       -2     
- Partials        795      800       +5     

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