Adding heuristics to locate libDBPATestAgent.* (used in tests)

[argmarco-tkd]

Adding heuristics to locate libDBPATestAgent.* (used in tests and github actions). In particular, this change helps Windows build locate the file.

Testing

• Local testing continues to work (Linux, via Docker, using ctest -L parquet)
• Github Actions for Windows no longer break because of the inability to locate libDBPATestAgent.dll
  • Before: https://github.com/protegrity/arrow/actions/runs/21967686817/job/63461580710
  • After: https://github.com/protegrity/arrow/actions/runs/22086585827/job/63822558721

[github-actions]

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Then could you also rename the pull request title in the following format?

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See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[sofia-tekdatum]

Saw the fix for the thrift problem in the next PR. Thanks!

[argmarco-tkd]

Saw the fix for the thrift problem in the next PR. Thanks!

should have mentioned it earlier - just for reference, this is the PR where that is fixed

#251