AthContainers: Fix coverity warnings.

Scott Snyderrequested to merge
ssnyder/athena:cov.AthContainers-20250624 into main
  • Don't allow exception to propagate through a destructor (CID 11789)
  • Avoid circular header dependency. (CID 17320, 17313)
  • Lock source store before copying (CID 11131)
  • Explicitly note discarded return values. (CID 13362, 17194)

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