Reuse HTTP connections across Azure clients

[uhc7]

Closes #276

Summary

Reuse HTTP connection resources across the core Azure SDK clients created by CloudClient to reduce connection setup overhead and improve sustained throughput for long-running workflows.

Changes

• Create a shared Azure Core RequestsTransport in CloudClient.
• Reuse the shared HTTP session across:
  • Batch Management client
  • Compute Management client
  • Batch Service client
  • Blob Service client
• Give each Azure SDK client a non-owning transport wrapper so closing an individual client transport does not close the shared session.
• Add CloudClient.close() to explicitly clean up the shared HTTP transport.
• Add tests covering HTTP session reuse and cleanup behavior.
• Bump the package version from 1.1.0 to 1.2.0.
• Update the changelog.

Validation

• Focused CloudClient/client factory tests: 48 passed.
• Targeted pre-commit checks passed, including Ruff, formatting, TOML validation, whitespace checks, and secret detection.
• Full test suite: 274 passed, 1 failed.
• The remaining failure is an existing Windows-specific test issue in test_download_job_stats, which uses the Unix /tmp/job-stats.json path and is unrelated to these changes.

[ryanraaschCDC]

looks good to me! I added @xop5 to review as well